Changed ERC20 .sol files' syntax and formatting

[Luiserebii]

Hello,

I felt that the expanded version that OpenZeppelin uses is difficult to read, so I changed it to a more legible version that is more "compact" and easier to trace from left-to-right. This has been done for ERC20.sol and IERC20.sol.

Aside from formatting, some variable name syntax has been changed; I personally feel that prefixing local/internal vars with underscores ("_") helps greatly with readability, since it becomes very clear which variable the permanent ones are. Perhaps the only inconsistency is with persistent private variables being denoted by "_", which now no longer have it, which could imply public variable depending on the way you see it. Perhaps adding a _ as a suffix for the parameters where they conflict with internal names...? (the doc "Style Guide" suggests the "_" suffix as a valid idea, see https://solidity.readthedocs.io/en/v0.4.25/style-guide.html under "Avoiding Naming Collisions").

Avoiding Naming Collisions

- single_trailing_underscore_

This convention is suggested when the desired name collides with that of a built-in or otherwise reserved name.

Finally, TNetToken.sol has been created, extending from many of the ERC20 OpenZeppelin contracts such as ERC20, ERC20Detailed, ERC20Mintable, and ERC20Burnable. I realized that a neat solution to keep a pre-defined "constant" name, symbol, and decimal would be to override the constructor and just define it there. I think it fits in with multiple inheritance in Solidity...?

Please let me know what you guys think about this. Thanks!