Added complete Java implementation of the MATH standard library
Added test revealing problem with unary minus of a binary expression
Fixed problem with unary minus of a binary expression and did some code refactoring to reduce code duplication
Utility method for isolating an expression (missing file on previous commit)
Added test revealing problem with generation of the subtract expression
Fix for problem with generation of subtract binary expression
Added test for div operator (integer division)
Added generation of div operator (for integer division)