2.0.0

• split the module into several files
• add issue and pull request templates
• a lot of code refactor and optimizations
• MSS: rename save_img() to to_png()
• MSS: save(): replace screen argument by mon
• Mac: get rid of the PyObjc module, 100% ctypes
• Linux: prevent segfault when DISPLAY is set but no X server started
• Linux: prevent segfault when Xrandr is not loaded
• Linux: get_pixels() insanely fast, use of MSS library (C code)
• Windows: fix #6, screen shot not correct on Windows 8