Improve CartoDataFrame documentation

[alasarr]

We need to improve the reference: https://carto.com/developers/cartoframes/reference/#heading-CartoDataFrame

• Add example for to_carto

• Description for set_geometry and set_geometry_from_xy

• Remove from doc astype, merge, dissolve, explode

[elenatorro]

Although this should be really easy to add, I did a quick test on develop branch and I got some sphinx errors when building the docs, they're really easy to solve cause they're related with the format (for example: Bullet list ends without a blank line; unexpected unindent.).

When testing it, please remember to run them locally to see if there's any format error and check the final result :) The instructions to run docs locally are here.

[Jesus89]

Elena, can we mark somehow the functions to skip the doc generation for the Dev Center reference?

[elenatorro]

Sure! it should be done by using :exclude-members: method_name in the .rst input file.

There's an example in the cartodataframe.rst file where we're skipping the convert method.