Like I said, I don't know very much about SBT's internals but before this patch,
1) The key wasn't exposed. _(meh)_
2) Going from key to string isn't just `key.value`, its `Project.showContextKey(state.value)(key.value)` which means you need to expose `state` as well and have special knowledge that I wouldn't have had to get a string out.

In light of that, what do you think?