Implement APCIterator

Implement a basic version of APCIterator
I tried to match most of php, but
it does not match php5 completely due to for example not implemented functions.
Inheriting from this class most likely won't exactly match php due to valid() calls in some methods etc.

However this is an implementation that passes all (but one) zend tests and thus matches general php behaviour
It works in all basic usages.

I use apc_cache_info() as the interface between C++ implementation and PHP
That function spits out all the information that our APC implementation has implemented

Currently unsupported is:

 * most of the format flags due to them not being implemented at all in C++
 * * working flags are: type, key, value, mem_size, ttl
 * chunk_size does nothing, because I don't save the data in my class
 * list because not implemented in C++ (I believe)

Closes #406