Use hidden value instead of internal field

Just a preparation to mix the array access stuff with the name-based
property accessors.
Move PHP to JS object wrapping into seperate file
Split php_v8js_hash_to_jsobj into smaller pieces

php_v8js_hash_to_jsobj is called for all wrapping to JS objects, be it
a PHP associative array or a PHP object.  I've now splitted both parts
into seperate functions since they don't share any code any longer
anyways.
Export extra methods on ArrayAccess

This merges the distinct code path for the export of ArrayAccess
capable PHP objects back into the "common" PHP object export code.
Sole difference is that the ArrayAccess-style object has index
property handlers as well as property bridging to Array.prototype.