Add storeid_file_rewrite helper

Add storeid_file_rewrite helper

Based on work by Eliezer Croitoru <eliezer@ngtech.co.il>

This program acts as a Store-ID helper program, rewriting URLs passed
by Squid into storage-ids that can be used to achieve better caching
for websites that use different URLs for the same content.

It takes a text file with two tab separated columns.
 Column 1: Regular expression to match against the URL
 Column 2: Rewrite rule to generate a Store-ID

Rewrite rules are matched in the same order as they appear in the file.
So for best performance, sort it in order of frequency of occurrence.