there are none. its fine to pull master from we. i would hope that script authors would always keep their master branch nice and clean.
if you must be on the bleeding edge of norns, be prepared to recompile. (master should always be buildable with a single call to ./waf. we aim to avoid other long-lived development branches; currently there is one just b/c various links point at it.)
norns-image is not something you should pull unless you want to contribute to linux / kernel configuration - wait for updates.