research feature: tracking branches taken to form branch probabilities

I admit this is more of a research feature request, but I put it in because the FuzzBench setup would seem to be a good way to get the data. I am not sure if this data is already being gathered through one of the other coverage calculations, so please forgive me if they are. The idea would be to track numbers of times different branch paths are taken, independent of entire path of execution to that point. These can be used to form branch probabilities and could be an interesting way to investigate/find rare paths or why a path is rare for all the fuzzers but 1, etc.

I apologize if this exists or I missed another ticket. This may relate in some way to #42 Further, since this is a research feature request, I do not expect it to be high priority. I just wanted to get it known or find out if that information is there to be found.