More diverging colour maps

[MBravoS]

Our initial selection of diverging colour maps was rather opinionated, with only some colour pairs used (based mostly on personal preference) and biased towards maps that diverge from black (uniform maps that diverge from white are more common). We should expand our selection to any colour pair that is friendly at least at least for green-red colour blindness, as there is no good reason not to.

[AstroRobin]

Added four new diverging colourmaps in v0.4.0, including BwG, CwO, PwO, YkB.

[MBravoS]

@AstroRobin any particular reason for using a different lightness dynamic range compared to the previous diverging colour maps?

[AstroRobin]

The issue really comes down to the fact that for, at least, OwC and OwP, it is almost impossible to get a set of extremely dark oranges without looking way too brown. The current dynamic range is set from 20-80 which sacrifices consistency in the central grey/white but gives what I think is a fairly nice colour map.

Happy to remove these if we don't think they can be improved given our constraints

[MBravoS]

I have added a bunch of new black-centred diverging colour maps (BkO, BkT, GkM, OkM, PkM, PkR, PkY, TkG, TkP, TkR and TkY). I think several work fine, but I'm fully convinced about the colourblind friendliness of some (GkM, OkM, TkP and TkR), and PkM/PkR may be too close to each other, what do you think @AstroRobin?

[MBravoS]

Expanded also the selection of white-centred diverging maps with v0.8.0. I think with the current selection we can close this issue.