Miner

Added a convention for threaded functions.

Added a purely notification based subscription to the state, I'm going to deprecate the other kind. Except that my plan for doing atomic reads on the state has failed, I'm not sure what the problem is. I'm really confused by the deadlock that's happening and would like you to review it and see if you have any ideas.

sia/miner.go got removed, the daemon doesn't need passthrough functions anymore because it has the miner directly. The core now only talks to the miner so that it can pass block updates on to other modules. This will also become unneeded after I finish my series of changes, and we will probably be able to drop the core altogether.

Right now there's a decent amount of legacy code. It'll all get removed soon enough.