fixed word boundary by using \b instead ([\W\s]?) and add RegEx support

[RobKehl]

Hi Jonathon!

First of, let me thank you for your plugin, it just works, which is great.

In this pull request I offer a fix for the problem where a token does not get replaced when it is at the end of the title. By using \b instead of ([\W\s]?), replacing works.

Cheers,

Rob

[RobKehl]

The second change is about adding RegEx support.

The admin is now able to use a regular expression in 'Match' and the eventually corresponding backreferences in 'Replace'.

That would allow this sort of match/replace-Bombshells to replace telephone numbers with tel:-links automagically:

s/((+|00)?([0-9]{2}-?)?[0-9]{3,5}( +)?(-|\/)( +)?[0-9]+)/${1}/i

For sure there are other things one could do with REs in this plugin, and the user is able to choose between REs and plain text. I thought it could be a valuable addition.

I submit it in chain to the former pull request, because it depends on it: The use of \1 and \2 in your original code would render the backreferences in 'Replace' invalid, and my change 8c11d19 makes those not necessary anymore and thus frees the way to using REs.

Cheers,

Rob