Now that have code highlighting enabled, we need to determine how 'automatic' it should be.

The code highlighting engine works in two ways:

1. Automatic inference of the language in use via the tags on the question, and
2. Manual specification of the language in a code block, overriding any language behavior on a question tag

Currently, we have highlighting enabled for a large number of tags, a default set from Stack Overflow or some such. We've already disabled automatic highlighting on a small handful (ios, iphone, php) due to awkward highlighting on questions, but we need to decide what approach to take for a consistent behavior across all tags.