Performance and testing 2
Just some brief stuff. Meant for this to be larger, but poloniex asked for another feature - indicate the miner fees in the outputs of a transaction. That has been added.
There's also a typo fix, and a benchmark for unmarshalling empty blocks. I had started to optimize that a bit, but ran into problems with MarshalSia and UnmarshalSia that we discussed.
Because we are upgrading a lot of the persistence stuff, we should probably address the MarshalSia and UnmarshalSia things sooner rather than later.