VitRegex - New Regular Expression (Regex) engine for Clarion

Version 1.18 of VitRegex is released

 - change to allow leniency where group name is given as a number.
   Some regex engines allow an alternative syntax ${1} as a numbered
   reference so that has been implemented now in VitRegex in addition to the
   normal $1 form.

 - fix bug where variable lookbehind was not constraining end position.
   The lookbehind sub-match needed a hard end position constraint passed into
   tryMatch. This required a new optional parameter on tryMatch such that the
   candidate start position *and* the required end position are both enforced.

 - lots more tests added