RegExp rework - part 05

This is a final part of PR #3223. (Other part are PRs #3433, #3434, #3435, #3442)

It's built on top of all other PRs, so [real changes](https://github.com/Karlson2k/xbmc/compare/regexp_rework_02_04...regexp_rework_05?expand=1) are smaller that they appear. 
This PR add some doxy and constructor overload to create CRegExp object and compile regexp at the same time (most common scenario in XBMC code - create and immediately call RegComp, now it combined in one step).