Updated docs
Updated todo
No need for specialized Type (bool, int, str, etc.) classes to represent type keywords, a simple enum will do.
Re-organized package structure
Renamed package 'evaluate' to 'eval'
Updated todo -> readme
CF
Extended test cases for typechecker. Fixed issue with undefined identifiers in expressions.
Updated todo
Created typeinitializer class to create generic value objects of different types.
Merge branch 'master' into martyn82
Removed commented-out constructions