Add support for modifying entity inside handler

$this is now bound by reference, so things like $array->pop() can
work properly.
Try fixing Travis CI once again

Probably they updated their PHP version and now the path is incorrect.
Trying out the `which php` variant in hopes that they fixed their
issues.
Add link to Windows DLLs
Added an array handler and implemented a bunch of array methods.
Implemented some more array methods.
Added push() and pop()