Support shortdocs for cog commands

[davejlong]

When outputting the help page for Cog, it would be useful to see a "shortdoc" for cog commands.

For example, on the Twitter bundle, the output of @cog help twitter is:

> **Commands**
>
> * `tweet` - Tweet from one or more accounts

It would be more user friendly if the format included the basic syntax of the command:

> **Commands**
>
> * `tweet` - Tweet from one or more accounts
>    * `twitter:tweet [--as <as>] <message>`

[ohaiwalt]

We can do this now by including them in the description field in the bundle config.yml, can't we?

It is unclear that's possible without some fussing though.

[nmohoric]

Since we already have an examples field we could probably loop through the non-empty lines and add this. Since this is a text field I do worry about existing stuff not being formatted correctly and becoming a mess.

Maybe we make it so the examples field accepts a list as well (at least for now). A text examples field will just throw the whole blob under there (or maybe not show at all), and a list can individually list them out. This would allow us to slowly transition existing stuff.