Improve single-line comment heuristics again

Single-line comments should now be validly detected in almost all
cases - the 'channel name' case will only be allowed if directly
succeeding '(' or ',' - this should be the normal way string-less
channel names are used. Preceeding ']' is included to allow for
array lengths

Closes #6 / https://github.com/OmegaPhil/geany-kvircscript/issues/6