Got addition working in grammar (first time without infinite recursion)
More MathematicalExpression rule working.
Added most of the mathematical functions supported by LinuxCNC
Added LinuxCNC.cpp/h as one example of a GCode object (uses GCode as the base class).

Got comments working in the LinuxCNC gcode parsing class.
Made it all the way through our first sample GCode file.
Copied more code from HeeksCNC::gcode_parser.cpp and parser.y