Update effect class, generation functions, add 2DAs and examples.

Effect Class:
- Add Get/Set functions for Float/Object/String effect values.
- Remove Versus functions.
- Fix GetIsValid to check validity directly rather than going through the NWScript stack.

Effect creation:
- Move all non-allocation operations into Lua.
- Fill in all empty effects.

NWNX Effects module:
- Remove obsolete item property stuff.
- Expand documentation of RegisterEffectHandler
Merge branch 'feature/effects'