Classes for Primitive Values

The framework for finding the class of primitive values is now in place.
A rudimentry implimentation of the Number class (for integers) is also now
set.

The REPL now by default loads a file `base/base.sap` from the current
directory.  Obviously there will need to be more intelegence about how to
find the standard library once we move towards a release.  Many values now
need to have their default base class written.

BUG FIX: insertLHS did not impliment LCVar but `def` depended on this for
adding class methods.