Issue #62: Refactor meat.py

Moved meat.py => address.py
Removed all references to meat.
Removed rawPubkey and rawPrivkey and replaced them with functions that calculate them on the fly.
Removed the b58_encode/sha256/md5/ripemd160 functions and started using the pycoin equivalents
Merge pull request #63 from jimmysong/62

Issue #62: Refactor meat.py