* Updated code style to no more than120 characters per line.

* Unify code comments style with Doxygen-style tags.

* Fix the conflicts.

* Add a return value in the contract ERC20Burnable.

* A Add a wrapper function to change type of address to address payable.

* U Modify Address utils.

* A Add test case for Address.

* U Modify code style in ERC20Burnable.

* Add changelog entry.

* Improved dev docs.