* Merge GSNContext into GSNRecipient

* Update GSNRecipient.test.js

* Update GSNRecipient.sol

* Make GSNRecipient inherit from Context

* Improve IRelayRecipient docs

* Fix link

* Update IRelayHub docs to the docsite format

* Update IRelayRecipient docs to the dociste format

* Fix typo

* Improve GSN readme

* Fix link

* Update GSNRecipient docs

* Apply suggestions from code review

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

* Apply suggestions from code review

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

* Apply suggestions from code review

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

* Replace confirmRelayedCall with approveRelayedCall

* Update gsn-bouncers.adoc

* Update deprecated enums

Bumps [mixin-deep](https://github.com/jonschlinkert/mixin-deep) from 1.3.1 to 1.3.2.
- [Release notes](https://github.com/jonschlinkert/mixin-deep/releases)
- [Commits](https://github.com/jonschlinkert/mixin-deep/compare/1.3.1...1.3.2)

Signed-off-by: dependabot[bot] <support@github.com>

* added tests for getApproved

* added tests for getApproved

* added to changelog

* Corrected some linting issues

* Removed unneccrary tests as pointed out here: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1820/commits/b49c2de086621745955be83a34a06de65e95c76c#r307927816

* Correct Changelog character

* Update ERC721.behavior.js

Bumps [eslint-utils](https://github.com/mysticatea/eslint-utils) from 1.3.1 to 1.4.2.
- [Release notes](https://github.com/mysticatea/eslint-utils/releases)
- [Commits](https://github.com/mysticatea/eslint-utils/compare/v1.3.1...v1.4.2)

Signed-off-by: dependabot[bot] <support@github.com>

* Adding in "<<: *defaults" under "coverage"

* Refactoring by capturing similar setup commands into single alias

* Reverting changes, I am not certain exactly how to refactor these setup steps, but at least the &default refactor can be made.

Fix typos in instructions

* Remove SignatureBouncer

* Update changelog entry

* Fix coverage

* Update CHANGELOG.md

* move gsn link

* change underscore to dash

* add content to gsn api ref

* change link of GSN announcement

* Update contracts/GSN/bouncers/GSNBouncerERC20Fee.sol

Co-Authored-By: Nicolás Venturo <nicolas.venturo@gmail.com>

* fix crossreference to gsn guide

* Remove intro from gsn guide

We are moving the intro to the top-level in the docsite, and focusing this guide into writing gsn-enabled contracts.

* Update docs/modules/ROOT/pages/gsn.adoc

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

* Update gsn.adoc

* 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 👍