1.9.0b5

Preview of 1.9.0.

Changes since 1.8:

• REQUIRE PYTHON >= 3.5
• Switch to distribution as a pip package! You can now "pip install simplemonitor"
• Add memory monitor
• Add Ring doorbell monitor (checks battery level)
• Add support for checking file is not too large
• Add support for running a command when a monitor recovers
• Add support for reloading config on the fly
• Fixes to compound monitor logic
• HTTP monitor can check both return code and regexp now
• Update pkgaudit monitor to chase new output format
• DNS monitor can check response is NXDOMAIN
• Many code quality improvements (I hope)