add github repositories sidebar plugin

if you specify

github_user:

in you _config.yml and once you add asides/github.html to your sidebar
items, this plugin will fetch the specified users github repositories
and order them so the last pushed ones are shown first. Then it'll list
them in the side-bar, including a link and the repository description

The plugin will only list your own repositories, not forks, though this
might need to be configurable later
allow limiting the amount of repos to display

by setting github_repo_count to someething that's not 0, you can limit
the amount of repositories to render
provide an option to show or not show github profile link
make listing/not listing of forks configurable

some people have more or less taken over projects with their forks, so
it probably makes sense to still list them among the repositories
corrected fork skipping logic
Static Server based on Sinatra

Using Sinatra provides better handling of mime types and supports
304's/etc.

Also updated the Gemfile to exclude most gem outside of developemnt
(default).
Fix broken line height in diff syntax highlighting
fixed bug with twitter feed where it would sometimes say "undefined" if the post was more than a month old
fixed bug where update_source Rake task was not copying over changes from .themes
Added prompt for overwriting posts and pages when a new_post and new_page tasks are run and the file already exists. Fixes #130
Improved support for non Latin characters in category names. Fixes #128
Merge pull request #127 from tobym/master

Fixes issue 126, broken line height on "diff" syntax highlighting
Merge branch 'github-repositories-plugin' of https://github.com/pilif/octopress into pilif-github-repositories-plugin
reverted back to \W in category_generator. Tracking on #128
Merge branch 'master' of github.com:imathis/octopress
added github asides to the default asides list
changed order for Github 3rd-party configs
Merge branch 'pilif-github-repositories-plugin'
use semantic HTML5 element for Google +1 button, see: http://code.google.com/intl/en-US/apis/+1button/#plusonetag
datetime must be valid date format, see: http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#concept-datetime