Maptial

Included radient in critical point analysis, using <0.75 so it is not too sparse.

Added a new derivative, with 3 which is critical point, where:
We can use a simplified numerical scheme to itemise these as our values.
I have called this `derivative` the criticalpoint. Where the gradient is not close to 0
the colour is 0, so there is a 5 colour scheme:
- -3 -> (3,-3)
- -1 -> (3,-1)
- 0 -> NA
- +1 -> (3,+1)
- +3 -> (3,+3)

Added prometry code in a decision to merge all python code to a single library