A proposal to add categorisation to script metadata

Hi there,

When I first hacked together the [Hubot Script Catalog](http://hubot-script-catalog.herokuapp.com/) there were, I think, less than a hundred scripts. Going through each script was a pain, so I created the catalog to view them all as a single page.

Today, we're approaching 500, and the catalog itself is getting somewhat unwieldy. It would be nice to categorise these scripts, to make them easier to sort through.

I was thinking of adding a new, optional section to the script metadata: Tags. I'd like to support something like:

```ruby
# Commands:
#   it's a trap - Display an Admiral Ackbar piece of wonder
#
# Author:
#   brilliantfantastic
#
# Tags:
#   memes
#   image macros
#   humorous
```

As far as I'm aware, this shouldn't break any existing Hubot documentation parsing. If supported, I could use this to build categories to browse through on the Script Catalog.

If this sounds good to you, I'm happy to tag the existing ones to organise them and set the precedent for subsequent script submissions.