Transaction Pool (first bit)

I implemented a transaction pool, or at least the beginnings of one.

It doesn't get updates from the state, which means it'll never realize that it's using transactions which have been accepted to the state.

It doesn't add storage proof transactions to the transaction set. This is also a problem.

In this PR, there's a decent amount of documentation that got added. There is also a decent amount of moving things around, and a decent amount of new functionality.

I expect to finish up with the wallet and transaction pool functionality tomorrow, including some more tests and making the API functional again for the wallet and miner stuff.