Improvements to our documentation infrastructure

• The "missing text in diagrams in API reference" issue was finally solved. Diagrams now work everywhere, including the 0.7.9 and 0.8.3 docs.
• We have converted our README files to markdown syntax. Bitbucket now shows helpful overview content on our CEGUI and CEED repos.
• Our official documentation landing page at http://static.cegui.org.uk/docs was greatly improved. (kudos goes to Timotei for web design)
• The version switcher in API docs can now handle fragment components in URIs. You should no longer see any "Invalid request" fatal errors when switching versions.

We hope that you appreciate our continuing effort to improve our documentation and the infrastructure surrounding it.