Isolated extension environment

Changes:
 - Isolated the extension environment.
 - Refactored commands: init, generate, compile, install.
 - Cleanup of test project generated files.

So now Zephir can be pulled from Git and rebuilt without affecting the extension project.
Moreover, the extension project can be located anywhere on disk.
The init command takes a parameter <namespace>
The generate, compile and install commands must be ran within the
folder of the project.

Note: I'm not familiar with Travis so I've tried to adapt the travis.yml file to the best of my abilities, however I haven't tested it, sorry about that.

I'd be really happy if you could please consider this pull request as I'm very keen on using Zephir for some internal projects we have here in Mobli, but refactoring the environment would really help us getting the job done faster.
Thanks!