Make it possible to compile on Windows

[alexdovzhanyn]

Right now there is no way to run the blockchain on Windows OS. Preliminary attempts at getting this to work have resulted in failure when trying to compile eleveldb. Another attempt at doing this through distillery resulted in not having the correct erlang version on windows

[alexdovzhanyn]

We're going to kill two birds with one stone on this issue:

I've been looking into switching out eleveldb for a more performant option and came across libmdbx, which touts significant performance improvements. Initially I looked into this last year, but the db didn't have OSX support (which is my main environment), and that would have hindered development.

Recently, libmdbx has been updated with support for OSX. We can create bindings to this db and use it instead. This would both solve both our need to compile for windows (eleveldb is the only thing stopping us currently) and our desire to improve performance, and even lets us do concurrent reads from the DB, which would significantly simplify our database interaction code.