Fix 64-bit typelib issues on 64-bit python

This fixes a couple of typelib loading issues under 64-bit python. First, it will detect when a structure or union type defined for 32-bit is being used in 64-bit and disable subsequent consistency checks. Secondly, it defines a proper DECIMAL type, which fixes loading issues found in 64-bit typelibs.

Fixes #7, and several of the failures in #9.