* 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.
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