Add the default monospace font stack for <code> elements

Unfortunately <code> elements weren't getting the monospace font stack they
deserved so they looked a little out of place. :lipstick:
Fix grammar typo
Mention that `target_url` is required.
Merge pull request #469 from github/gjtorikian-patch-2

Mention that `target_url` is required.
Revert pull request #469
Merge pull request #470 from github/revert-469

Revert pull request #469
document permissions hash in repo descriptions
commits cannot be filtered by full name of author
Add head_ref_deleted as valid event

Not real sure on what to say here, but something is a start ;)
add head_ref_restored
Squashing and merging an update
Merge pull request #472 from github/update-1396638735

Opening a Pull Request for alternate updates
Sync changes from upstream repository
Merge pull request #473 from github/update-1396645501

Sync changes from upstream repository
updating a bunch of links to the developer site to be https
fix the documentation for github signature
Merge pull request #475 from konklone/fix_signature

Fix docs for name of GitHub signature request header
reverting incidental version qualifier
document search api incomplete_results attribute
Updating to use GitHub default font stack

- Make the <code> font stack more consistent from GitHub.com.
- Refactor code/pre selector rules to be generic enough to catch all
the lingering code blocks.