Document bitswap

Hey @dignifiedquire i have some questions re impl. Forgive silliness, first time i look at it.
1. why is bitswap block key going to hex in the proto msg? it should be straight binary -- https://github.com/ipfs/js-ipfs-bitswap/blob/master/src/message/index.js#L48
2. why bitswap.stop has this.network.start() https://github.com/ipfs/js-ipfs-bitswap/blob/master/src/index.js#L276
3. why bitswap.network uses bl? isnt this wasteful? is it caching all buffers? (i've only glanced at bl, havent used it) https://github.com/ipfs/js-ipfs-bitswap/blob/master/src/network/index.js#L40
4. `provierRequestTimeout` spelling - https://github.com/ipfs/js-ipfs-bitswap/blob/master/src/constants.js#L7