Extract category_link filter from category_generator.rb plugin

Allows category_link to be used as a filter to display a link to
any category.
Added robots.txt, with sitemap link
Example repo URL - see Github issue 516
Updated Github API to V3.

Github API V2 has been removed.  The response data format also changed.
Updated Github API to V3.

Github API V2 has been removed.  The response data format also changed.
Updated gems and rubies to 1.9.3
Fix for issue #622

The filters bundled with Octopress are not applied to files ending in
`.md`, because the match in octopress_filters.rb does not match `.md`.
bumped rbenv version fixing #743
Twitter API call and links are now protocol relative
Using https instead of protocol relative urls, for Pinboard and Twitter feeds
To support url without domain name like /path/file

You need to know if you would like to support this, each word in the title can not start with "/".
Fixing English error pet-peeve.
Rakefile option for any additional rsync arguments

Added variable `rsync_args`
gist tag plugin now works with the latest changes GitHub gists and does not fail if you do not specify a filename.
Titles in code plugins can have slashes in them. Closes #892
Removed unnecessary regex in code block plugin
updated gems
Rake task new_post now accepts titles through stdin
This should help resolve issues for zsh users and make it easier to enter titles which freak out Rake's argument processing
removed accidentally added file
Escape github repo descriptions, as they may contain HTML.