Un-reverse the bitcoin_hash type in memory

With this change, the reversal only takes place in the encode_hash
and decode_hash functions.
Merge pull request #144 from libbitcoin/reverse

Reverse bitcoin_hash in memory
Change --enable-debug to --enable-ndebug and config travis ndebug builds.
Fix ndebug builds (don't enclose release code in debug assertions).
Exclude parameters and vars not used in debug builds.
Fix VS project/filter.