Removed pthreads workarounds, new pthreads version

This branch removes some workarounds for some bugs in pthreads.
These changes allows code to behave as developers expect, without having to do special class loading steps.

The bugs fixed on pthreads are:
* References to objects in static properties on other classes are removed when starting a Thread krakjoe/pthreads#271
* pthreads leaks memory when using Threaded on Windows krakjoe/pthreads#289
* Removed several random memory leaks
* Increased overall performance and corner cases

These changes will be merged once a new version is released on [PECL](http://pecl.php.net/package/pthreads) and new binaries are compiled.

* [x] Bump required pthreads version on RakLib, PocketMine and Travis-CI
* [x] Compile new binaries and test Windows, Linux and MacOS
* [x] Remove IPC sockets for thread communication on RakLib
* [x] Remove IPC sockets for thread communication on Generation Thread