Create preg_match_all.js

Hello,

This is my attempt at preg_match_all in JS.
There are 2 functions in this file : `preg_match_all()` and `find_parens_sub()` : `find_parens_sub` counts the number of capturing parentheses in a pattern.

I didn't put `find_parens_sub()` in a separate file because it isn't a PHP function : it's a C function used in pcre_compile.c, used in php_pcre.c. Maybe it's better if it is in another file anyway ?

You can see a quick example here : http://jsbin.com/ruwanu/1/edit .
Or my full code with PHP tests here : https://github.com/Eartz/pregMatchAll.js