* Update gsn_advanced.adoc

Line 15 - where it says, "prevent malicious users from spending the transactions subsidy", with transactions subsidy, is it supposed to be possessive "transaction's subsidy" or is the plural in the wrong place "transaction subsidies"?

Line 176 - where it says "or it is not allowed to spend that amount". Is IT referring to the sender/person or the tx? If IT refers to a person, then change to "or they are not allowed..." for gender neutral.

Line 213 - Where it says, "Please not how the gas cost estimation", a verb is missing, please what?

* Update gsn_advanced.adoc

Apply suggestions by Amy

* switch to using Context internally

* add context import

* Add smoke test to make sure enabling GSN support works

* Update test/GSN/ERC721GSNRecipientMock.test.js

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

* Upgrade truffle

* add missing awaits

* Revert "Upgrade truffle"

This reverts commit f9b0ba9019650fdbf8919a33e6fba834689e6b04.

> openzeppelin-solidity@2.3.0 lint /home/luiserebii/github/openzeppelin-solidity
> npm run lint:js && npm run lint:sol

> openzeppelin-solidity@2.3.0 lint:js /home/luiserebii/github/openzeppelin-solidity
> eslint .

> openzeppelin-solidity@2.3.0 lint:sol /home/luiserebii/github/openzeppelin-solidity
> solhint --max-warnings 0 "contracts/**/*.sol", alongside some minor grammatical corrections

* Add base Context contract

* Add GSNContext and tests

* Add RelayHub deployment to tests

* Add RelayProvider integration, complete GSNContext tests

* Switch dependency to openzeppelin-gsn-provider

* Add default txfee to provider

* Add basic signing recipient

* Sign more values

* Add comment clarifying RelayHub's msg.data

* Make context constructors internal

* Rename SigningRecipient to GSNRecipientSignedData

* Add ERC20Charge recipients

* Harcode RelayHub address into GSNContext

* Fix Solidity linter errors

* Run server from binary, use gsn-helpers to fund it

* Migrate to published @openzeppelin/gsn-helpers

* Silence false-positive compiler warning

* Use GSN helper assertions

* Rename meta-tx to gsn, take out of drafts

* Merge ERC20 charge recipients into a single one

* Rename GSNRecipients to Bouncers

* Add GSNBouncerUtils to decouple the bouncers from GSNRecipient

* Add _upgradeRelayHub

* Store RelayHub address using unstructored storage

* Add IRelayHub

* Add _withdrawDeposits to GSNRecipient

* Add relayHub version to recipient

* Make _acceptRelayedCall and _declineRelayedCall easier to use

* Rename GSNBouncerUtils to GSNBouncerBase, make it IRelayRecipient

* Improve GSNBouncerBase, make pre and post sender-protected and optional

* Fix GSNBouncerERC20Fee, add tests

* Add missing GSNBouncerSignature test

* Override transferFrom in __unstable__ERC20PrimaryAdmin

* Fix gsn dependencies in package.json

* Rhub address slot reduced by 1

* Rename relay hub changed event

* Use released gsn-provider

* Run relayer with short sleep of 1s instead of 100ms

* update package-lock.json

* clear circle cache

* use optimized gsn-provider

* update to latest @openzeppelin/gsn-provider

* replace with gsn dev provider

* remove relay server

* rename arguments in approveFunction

* fix GSNBouncerSignature test

* change gsn txfee

* initialize development provider only once

* update RelayHub interface

* adapt to new IRelayHub.withdraw

* update @openzeppelin/gsn-helpers

* update relayhub singleton address

* fix helper name

* set up gsn provider for coverage too

* lint

* Revert "set up gsn provider for coverage too"

This reverts commit 8a7b5be5f942002710cba148f249cb888ee8e373.

* remove unused code

* add gsn provider to coverage

* move truffle contract options back out

* increase gas limit for coverage

* remove unreachable code

* add more gas for GSNContext test

* fix test suite name

* rename GSNBouncerBase internal API

* remove onlyRelayHub modifier

* add explicit inheritance

* remove redundant event

* update name of bouncers error codes enums

* add basic docs page for gsn contracts

* make gsn directory all caps

* add changelog entry

* lint

* enable test run to fail in coverage

* GSN Advanced guide

* Tweaks

* Apply suggestions from code review

Changed word from Destoys to Destroys in line number 220.
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol#L220

Need review. Thanks 👍

Fix typo

* replace readme badge

* remove travis config

* move to codecov

* add codecov config

* fix coverage running

* GSN basics guide (#1847)

* Fix linter error

* Initial draft for basic GSN guide

* Add CustomerAcquisitonCost link

* Review 'gas costs' phrasing

* Rename relay to relayer

* Apply suggestions from code review

Co-Authored-By: Santiago Palladino <spalladino@gmail.com>

* Improve transition to contract usage explanation

* Improve payment section phrasing

* Apply suggestions from code review

Co-Authored-By: Andrew B Coathup <28278242+abcoathup@users.noreply.github.com>

* Apply more review suggestions

* Add code

* Add unreleased warning

* GSN Docs Tweaks (#1860)

* Adjusts links

* Adjustments

* Update gsn.adoc

Fix typo

* Adjusts copy and links for GSN guide (#1865)

* Adjusts copy and links

* Formats links

* Adds website link

* remove attach_workspace

* leave default working_directory

* use npm ci for installing deps

* rename dependencies job

Fix typo

* Add circlci, remove .travis.yml. Fixes #1839.

* Fix circleci config

* Add slack notification

* Add circleci status

* Fix config.yml, we don't need separate truffle image and instances.

* Matches oz-sdk node version

* Seems node:10.13 doesn't work for CircleCI either

* Remove npm update in circleci

* CircleCI use package-lock.json as cache key and install only the lock version

* Add back travis.yml

* Rename job build to test

* CircleCI requires that job to be called build instead of test or build_and_test

* Fix the way to run jobs

* Fix CircleCI

* Change back to npm install

* Add workflow and split into tasks

* Add workspace

* Restore cache

* update readme circleci instructions

* make step name more accurate

* Imporvement: functions in SafeMath contract overloaded to accept custom error messages.

* CHANGELOG updated, custom error messages added to ERC20, ERC721 and ERC777 for subtraction related exceptions.

* SafeMath overloads for 'add' and 'mul' removed.

* Error messages modified.

* Update CHANGELOG.md

* added _safeTransferFrom function

* added safeMint functions

* added package-lock.json for consistency, don't know why it changes

* added initial suggestions/modifications

* change _safeTransferFrom to internal, reverted package-lock.json to original, and changed ERC721Pausable to override _transferFrom instead of transferFrom

* included tests for safeMint functions

* modified safeMint tests to be on ERC721Mock contract

* added safeMint to ERC721Mintable & respective test to ERC721MintBurn.behavior.js

* Rename package and repository name from docs and scripts

* undo root package rename

* add @openzeppelin/contracts as subpackage with release automation

* synchronize @openzeppelin/contracts version

* remove private field from package.json

* make file patterns absolute

* change wording of a comment

* use a saner version script

Add: Interface names should have a capital I prefix.

* add OwnableCautious with associated mock and tests

* extraneous comma removal and cleanup

* remove non-documentation changes from branch

Change URLs to openzeppelin.com

Update URLs and names to OpenZeppelin and OpenZeppelin Contracts

Update URL to openzeppelin.com