Unified plugin system

See merge request !2

Refactored the plugins to use a single Plugin interface.
Communication to and from the IRC server now happens via channels.

- RSS plugin now uses the unified plugin system
- Inserted .unwrap() to various error-sensitive pieces of code
- Cleaned up unused variables and imports

Refactored the plugins to use a single Plugin interface.
Communication to and from the IRC server now happens via channels.

Don't extract title if request is unsuccessful

See merge request !1

- Updated ureq to 1.1.1
- Only read the first 10KB from any URL to find title tags

- Included a Dockerfile that can build the project
- Updated ureq to latest

- GOLBot will no longer send titles when the title is empty or doesn't
exist