Add Venus relief cpt

[Esteban82]

I made the Venus Relief CPT.

I do it from this legend:

Link: https://astrogeology.usgs.gov/search/map/Venus/Magellan/RadarProperties/Colorized/Venus_Magellan_C3-MDIR_ClrTopo_Global_Mosaic_6600m

This is the map that I got:

For the record, I get the colors from the legend with:

# Get a figure of 1 px height along the center of the legend
gm convert $input -crop 1382x1+47+190 $perfil  

# Extract the colors in RGB format.
convert $perfil -depth 8 txt:- | tail -n +2 | sed 's/[ %]*//g' | sed -n 's/^\(.*\),0:[(]\(.*\),\(.*\),\(.*\)[)][ ]*\#.*$/\1 \2 \3 \4/p' > colors.txt

[joa-quim]

Something does not look right on the high value colors. This cpt looks almost cyclic and the image does not show the same colors as in the posted link.

[Esteban82]

Something does not look right on the high value colors. This cpt looks almost cyclic

Yes, I agree. Maybe we need another CPT or change this one a bit.

the image does not show the same colors as in the posted link.

In part, they might look different because they are from different datasets.

[Esteban82]

In the last commit I update the info for the GEBCOSI recipe and I add the version of the grids (SRTM15plus, GEBCO and synbath).

[Esteban82]

I complicated this PR by adding these last commits that are from another topic. I will close it and make another PR.