add ability to only instrument files that match a regex

I added the ability to only include files that match a passed in regex.  We use a decent amount of libraries and other .js files that we don't want instrumented.  To ignore all of the files that we don't want by using the --no-instrument-reg param would make us list 100's of regexes.  Having the ability to specify an only instrument regex allows us to have one simple regex.