Add GenericScalarFunction source and header file
Add ConstantScalarFunction source and header
Add BaseScalarFunction impl file
Pull out all classes and impls from ScalarFunction.h
Add make rules for all *ScalarFunction.{C,h} files
Add instantiation and includes to make examples compile
Add includes that make tests pass
Merge pull request #66 from dmcdougall/sep_impl_scalarfunc

Separate implementation of all classes ScalarFunction.h