Put MurmurHash3 in bitcoin.bloom
Mark internal script-eval machinery as private
Add more documentation text
Remove hashtype form EvalScript routines

Probably existed in the Satoshi code to check that a given hashtype
matched what was expected; removing for now until we have an application
that actually needs the functionality so we can figure out the right way
to do it, clean-sheet.

Also added some more documentation.
Rework EvalScript machinery to raise exceptions

Useful to determine just how and why a script failed.