acc-erc20 v0.5.7

ERC20

This is my ERC20 implementation. There are many like it, but this one is mine.

This ERC20 implementation aims to exactly follow the ERC20 specification, with no added features beyond the most basic ones. Its goals are to be correct, clear, and cost effective in terms of gas.

This ERC20 implementation borrows heavily from dapphub's DSToken. Mostly I've simplified and clarified it.