- Added diagnostic token dump to 'calc' in debug mode, after token substitution
so the new tokens can be seen.
- Added unit tests to look for parser syntax errors.
- Added test for '2--3'.
- TW-1254 Calc command can segfault on negative numbers (thanks to Renato
Alves).
- Implemented a recursive descent parser to syntax check the expression,
and disambiguate unary minus. The syntax checking is not generating any
diagnostics yet.
