clean up mining internals
add function to ReplaceMiner
put peer code into its own file
split channel stuff into its own file
change siad api for mining
fill out miner info struct
attempt to fix miner status reporting
fix miner status
fix miner front end
allocate one core per thread when mining
rename siacore package to sia
Rename Environment to Core

In some places, especially files that I intend to edit a lot, but also
in some files that should be more or less stable, I didn't change it
from e *Environment to c *Core, instead leaving it as e *Core.
change e to c for testing files
Merge pull request #182 from NebulousLabs/minef

Fix mining front end