git-nav-upstream, as well as introduce a generic 'depot_tools' manpage with a
listing of the other tools.

This change also fully colorizes the EXAMPLE sections for the git-* commands to
reflect their actual appearance on the console (html only, manpage has bolding
hints).

R=agable@chromium.org, szager@chromium.org
BUG=261738

Review URL: https://codereview.chromium.org/200903002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@259338 0039d316-1c4b-4281-b951-d872f2087c98