Various updates readying the site to go live

Updated category_links filter to tidy up duplicated category paths when there are 3 or more
categories linked to a post
Updated the Rakefile with the newly modified publish task and new global task used on other
sites
Deleted all unnecessary .html versions of each post
Started working through posts, cleaning up the Markdown and replacing image/gallery links
with flickr_image and flickr_photoset tags. Initially started working from the oldest, but
due to the dealine looming, started working backwards instead. Posts updated so far:
  - And we're packed!
  - A map of our travels in China
  - The journey begins
  - Our first day in Beijing
  - Rain and Silk Markets
  - Olympic village, Summer Palace and Bell Tower
  - Our first day in Mongolia
  - Nomads, Airag and Curd
  - Musicians, flooding and evacuation of site
  - The Eden Project