This should parse parentheses correctly and handle (valid) gcodes such as
G1X2Y3, while before we were assuming spaces between tokens (which is wrong as
per the G-Code spec). This should fix req #333 in a clean and systematic way.
This is also a component for #343 (Marlin M114 response is in the form ok C:
X11Y22Z33E44, which we can parse with the same expression).