Proposed LRUG site static page format & example use in index pages

This is an partial implementation for discussion of a new LRUG markdown page format for discussion - a test selection of files are present in /source/meetings/ and source/index.html.erb has been changed use this amended format.
 
Main changes to Markdown format and organisation:

* generate a category tag for every page and add to markdown YAML frontmatter e.g.

```    
category: "meeting"
```

* add all page specific html/md fragments to the main .md frontmatter file in a block scalar e.g.

```
sponsor: |
  [<image src="http://assets.lrug.org/images/rethink_logo_small.jpg" width="120" height="31" alt="ReThink Recruitment" title="ReThink Recruitment Logo"/>](http://www.rethink-recruitment.com/)
```

* make sure published_at is populated

* pre-pend folder & file names with date format that will allow listings to naturally appear in correct order e.g. 201201 for Jan meeting

### Questions

Can we just do away with the extended content stuff?