Polish documentation for MySQL, Apache, nginx plugins
Merge branch 'master' of https://github.com/scalyr/scalyr-agent-2
Added a --debug-level option for the run monitor.
Merge branch 'master' of https://github.com/scalyr/scalyr-agent-2
Fix false warning message about content disappearing.
Fix bug where incorrect error message was being printed when
a metric value of None was received.