[rss] Clean up code, fix commands
[rss] Clean up code, fix commands

- Cleaned up code, clarified docstrings and messages
- Tightened up command usage requirements
- Removed support for quoted feed names with spaces, for now
- Added a "clear" option to remove all feeds from a channel
Uname-a/knife_scraper,Uname-a/knife_scraper,Uname-a/knife_scraper