This PR refactors the unit tests to be functional for the adapters, instead of mocking them, to test their implementation - not the expected stacktrace. This PR also changes some other things, such as:

• Tests for dependencies have been removed
• StreamFactory moved from Adapters to File class
• new FulfilledPromise -> React\Promise\resolve
• new RejectedPromise -> React\Promise\reject
• PHP5 support dropped
• Bumped phpunit dep
• Travis will not use composer.lock (for obvious reasons, such as you can't use some old versions on latest stable PHP)
• No failures allowed
• Some getters added to AdapterInterface (counterpart to the setters)
• Useless classes and/or traits removed and/or merged into the class(es)
• The child process adapter will not use count anymore for the file descriptor - instead one will be generated using PHP7's random bytes API
• ls has been made to use a promise, instead of a stream (made compatible to the interface)
• The ambiguous variable names of symlink have been renamed to be not ambiguous anymore
• The type detectors will be used as necessary and only fallback to the other when necessary (to remove unnecessary iteration)
• Adds method defined in class to filesystem interface
• Remove opinionated usage of a specific adapter in stream
• Pthreads adapter implemented using CharlotteDunois/Phoebe for pthreads pool with messaging and event looped worker

The PR commits will be squashed once review is positive. This PR includes and closes #46.