Use pages for documentation, not posts, fixes #980.
Move the building of related posts into their own class
Move the require for related_posts to jekyll.rb
Wrap tests around Jekyll::RelatedPosts

This gives me more confidence that we're doing the right things when it
comes to both the LSI and non-LSI cases and prevents regressions.
Update the display of the LSI progress output

It now fits more in line with what the other messages display.
Also stub the building of the index

Since we don't actually use the index in getting the related posts from
the tests there's no need to build an index, which can take a long time
if the ruby bindings for the GSL library are not installed.
Added jekyll-contentblocks to the plugins list
new test case: numbers in categories
Add a `data-lang` attribute to code blocks
fix handling of number categories
adjust tests to new test post
Changed link to liquid, was going to a dead link and it really bothered me.
Corrected additional liquid link on the Welcome page.
Changed the liquid link in posts.
Changed liquid link of the homepage.
Merge pull request #1073 from zachgersh/link_change

Changed link to liquid, was going to a dead link and it really bothered me
Update history to reflect merge of #1073.
Merge benbalter:docs-pages #985
Update history to reflect merge of #985. Closes #980.
Make Upgrading docs page a Page.