[imp] Removes deprecated option

Auto-regeneration is now set using the build/serve flag --watch

See: http://jekyllrb.com/docs/usage/
[imp] Standardises and improves xml format.
[imp] fixes and optimises footer links

Switches .xml link to an absolute so it isn't broken everywhere other
than the homepage and removes redundant http: from external links.
[fix] Reverts earlier commit

Escaped strings are formatted as <pre> by MD parser. Switching MD
parser to Redcarpet resolves previous build issue.
[imp] Sets RedCarpet as default MD parser.

The default Maruku is pretty fragile and standard characters in .md
frequently breal the build process. RedCarpet seems far more robust.
[imp] Adds post excerpts

Since I first authored this Jekyll has added support for automatic
posts excerpts. This change implements them in the archive view.