Converted code to use ESI
Split out Compatables.class.php file

* Also added missing config file
Added $wgCompatablesJsonFileUrl and made various cleanups
Set TTL in Cache-Control header for special page
Fixes for older PHP versions
"<!DOCTYPE html><html>" was showing up in the final html
Merge pull request #4 from AaronSchulz/master

Support ESI tag in CompaTables, improve extension structure