Minus in Identifier
This patch add "-" as a regular char in identifier, e.g. a rule name can be
For expressions, this clashes with arithmetic operator
-a == (- a) -a-b == (- a) - b
It also repairs a bug that
- a - b is interpreted as
- (a - b)
The error check for assignments is missing, e.g. "a-b := 1", and is left to reader.