Removing hash_table.h

[Quincunx271]

hash_table.h is a rather large file (900 lines of code). Only one of the types, BinHashTable, is used, and only in one place (enumerator.h / enumerator.cpp). Together with hist_table.h, this appears to form the history hash table.

What data structure is BinHashTable? If we can understand it well enough, we may be able to replace it with llvm or standard library data structures, removing quite a bit of otherwise unused code.

[kerbowa]

It's an implementation of a hash table. We should be able to replace it. This was on my todo list, hopefully I get the time to work on it.

DenseMap or something should work http://llvm.org/docs/ProgrammersManual.html#map-like-containers-std-map-densemap-etc