implement general concentration potential routine
add a _scale to all current potentials for which this makes sense
add a _scale to all current potentials for which this makes sense
add a _scale to all current potentials for which this makes sense
add _scale requirement for potentials to docs
add conc to API docs
fix scale in Miyamoto-Nagai
fix propagating H and Om
initialization of NFW potential with concentration and mass
add new NFW initialization to changelog