Added support for <time> - <time> +. Closes #28.
Fixed special case for <time> - <time> +. Related to #28.

Issue was that time ranges starting outside of the current day are not
accepted (e.g. 24:00-03:00) but with extended open end something like
'11:00-24:00+' could be used which seams to be totally validate but it
was not interpreted correctly because the time range function is called
recursively to evaluate '24:00+'.