Break require into multiple lines.

[MicahZoltu]

https://github.com/Uniswap/uniswap-v2-core/blob/d2ddbd95e8500cfd3669ab81b64f48956521ea6b/contracts/UniswapV2.sol#L39

This require statement is pretty gnarly and difficult to grok. Consider breaking it up into multiple require statements like:

require(success, "UniswapV2: TRANSFER_FAILED");
require(data.length == 0 || abi.decode(data, (bool)), "UniswapV2: TRANSFER_FAILED");

A comment here also wouldn't hurt to improve readability, something like:

If the function returned something, assume it was a success flag and check to make sure it is true.

[MicahZoltu]

Note: This is basically the same as #32, but I wanted to call it out specifically since it is particularly gnarly code and worthy of at least a comment I think, if not the separation.

[NoahZinsmeister]

closing in favor of #32 , let's be consistent with how we handle all of these