add 'get betterlink' link in nav
add placeholder navs for contributing via github

- create 'Developer' dropdown menu
- add link in Docs index
re-enable linking directly to FAQ answers

We want to enable this so that we can later highlight content and link
directly within a FAQ answer.

If either of the default code sample links are selected, clear out the
URL's hash.
add canonical links
update betterlink.js call to handle page hashes