Multiple tests supports, example tests, osx support, makefile added

Having multiple tests support is pretty hand also as installation for osx and linux through makefile.

* Modified all path's so all of them would be detected automatically.
* config.py allows to add multiple tests
* Added 2 example which allows to do multiple-viewport screenshots, and single screenshot.
* Added Makefile which detects OSX and Debian/Ubuntu and install everything for you with just one command
* Updated README.md with instructions
* runner.py: osx support added