Rework help system (again) to reduce channel noise.

Attempts to follow the discussion in #14. 

.help would output:

```
00:01 < rwjblue> .help
00:01 < turbot_> Hi, I'm turbot. I know how to respond to many commands (I also accept pull requests for more). For more information on any of them execute .help <command name>.
00:01 < turbot_> '.chuck norris', '.chuck says', '.chuck', .cowsay, .rule of acquisition, .gem <search term>, .gem info <search term>, '.github status', '.github last message', 
                 '.make me a sandwich', .nextmeetup, '.joke me', '.joke', .turbotinfo, .ddg, .help
```

.help <some matcher text> would output:

```
00:01 < rwjblue> .help chuck
00:01 < turbot_> '.chuck norris', '.chuck says', '.chuck' - Rockin' Norris Quote
00:01 < rwjblue> .help chu
00:01 < turbot_> '.chuck norris', '.chuck says', '.chuck' - Rockin' Norris Quote
00:01 < rwjblue> .help .ddg
00:01 < turbot_> .ddg - Search Term = Perform DDG search.
00:01 < rwjblue> .help .ddg
00:01 < turbot_> .ddg - Search Term = Perform DDG search.
00:02 < rwjblue> .help .joke
00:02 < turbot_> '.joke me', '.joke' - Random joke from reddit.com/r/jokes.
```