2.0.18

• new contributor: @cycomanic
• change license to MIT
• Linux: remove MSS library
• Linux: insanely fast using only ctypes
• Linux: skip unused monitors
• Linux: use errcheck instead of deprecated restype with callable (fix #11)
• Linux: fix security issue (reported by Bandit)
• add type hints
• add documentation (fix #10)
• add tests and use Travis CI (fix #9)
• remove unused code (reported by Vulture)