#37 Add arithmetic functions

[Kevin Rogers]

MillScript is currently missing the simple arithmetic functions, i.e. -, +, *, etc.

This can trigger an obscure bug with subtraction, e.g.

var x = 7;
x - 7;
There is 1 result
0

x- 7;
There is 1 result
0

x -7;
MISHAP : Could not find the definition for this variable
NAME : -
ORIGIN : origin
LINE NO. : 2
PHASE : Compile
Resetting input and resuming execution

x-7;
MISHAP : Could not find the definition for this variable
NAME : -
ORIGIN : origin
LINE NO. : 5
PHASE : Compile
Resetting input and resuming execution

This happens because the "-7" gets parsed as a negative integer, when it should be "- 7". The way this is dealt with in MillScript requires that the subtract function exists and is bound to "-".