Add search for assignments.
Add full-text search for assignments.
Add more sample assignments.
Speed up assignment search.

* Combine searchable fields into a single column and index it.
* Use a trigger to keep the searchable field up to date which
  requires switching from db/schema.rb to db/structure.sql.
Display query on search results page.
Fix code block rendering.

The HTML tags being generated were not balanced.
Merge pull request #12 from atsheehan/search

Search