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 #1427
closes #1508

fixes #1102

closes #1054

This affects tags in the following plugins:

- cassandra
- disque
- rethinkdb