Add rdiscount and RedCloth to Gemfile

`bin/build` fails without them.

Also s/:rubygems/https://rubygems.org to prevent deprecation warning when bundler fires.
Corrected submodule path for presentations/, accidental absolute pathing from dev box
Merge pull request #79 from benbalter/gh-pages

Make path to presentations/plugins submodule relative
Merge pull request #81 from github/submod-fix

Corrected submodule path for presentations/, accidental absolute pathing...
Merge pull request #80 from benbalter/gemfile

Add rdiscount and RedCloth to Gemfile
Subject/verb agreement (as I read it)

“GitHub” is consistently referred to in the 3rd person, and I thought the sentence reads better when that is maintained. Also, switched straight quotations marks to typographic ones, because why settle for less?
Removing duplicate h1 with title

The bare.html layout file already outputs the page.title as an h1, so blog posts currently get duplicate titles (see [Refactoring](http://teach.github.com/articles/Refactoring/) or [Materials launched](http://teach.github.com/articles/Materials-Launched/))
Merge pull request #85 from acusti/patch-2

Removing duplicate h1 with title
Merge pull request #84 from acusti/patch-1

Subject/verb agreement (as I read it)
Update h3 style and alignment
Merge pull request #86 from github/update-h3-styles

Update h3 style and alignment
New theme and organization of styling presentations
Added theme in Front Matter for individual slide deck page
Inverted logo graphic colors to bright white
Moved original slide deck theme files to new theming structure
Added per-slide-deck front matter and removed from template layout
Added slide deck default theme fallback
Adding page for spanish resources as dicussed in #83 (and #82)
Adding page "Othe languages" to courses category
Merge pull request #88 from aprendegit/spanish_resources

Adding page for spanish resources as dicussed in #83 (and #82)