Prefer using force_as over reinterpret_cast
Cleanup Dispatch usage and remove unused versions
Use nil<> template over explicit casting of cNil
Use RBOOL and CBOOL where appropriate

In a lot of places we used ? : or multiple return style to return Ruby
boolean values. We have a helper for that, RBOOL so we might as well use
it. Also switch to using CBOOL where it's appropriate for Ruby to C(++)
boolean checks.
Fix space after if() to match style guide
Move leopard_hashtable to proper name