Book review WIP

I've done a bit of work on this, main things are

* moved book-review out of lrug-root to correct place in site structure
* extracted base layout into it's own template, made other templates inherit from base
* changed format of reviews .md files to have a `excerpt` key which is a multi-line string and use new layout
* created books and book-review layouts

Questions:

* Are the review .md format changes etc. ok?
* We need to re-org the reviews folder structure to get the same URL scheme as the current site (http://lrug.org/book-reviews/2008/10/05/railsspace-tutorial-dvd-1/) - can we do this via the Radiant export script of should I just do this by hand?