Hash table initial implementation.  Has bugs.

Search is now progressive over multiple depths up to the target depth.
Will give better results for partial and interrupted searches.
Abort() conditions replaced with Die() conditions with more explanatory
text
Hashing is not working correctly -- set/get of hash values is incorrect
at the Set level.  Needs to delete previous piece from hash before
inserting new one.
Cleaned up some old comments.
Dieing does not automatically abort now.
Output more UCI friendly.
Hash table sort of working, hashfull parameter added

Redesigned hashing logic, seems improved but not proven yet.
Added engine-shootout.bat
Added hashfull parameter to uci reporting