in this commit:
- centralize logging output handler.
- set global Info/Debug/Error log levels based on config file or flags.
- remove per-plugin debug arg handling.
- add a I!, D!, or E! to every log message.
- add configuration option to specify where to send logs.
closes#1786
closes#1542
Generalize event.
Add doc.
Update default config.
Add filestack to the list of plugins.
Check that video conversion event returns 400.
Update the readme.
Update the changelog.