Write the developers documentation of the following files

https://github.com/pgRouting/pgrouting/blob/develop/src/common/points_input.c
https://github.com/pgRouting/pgrouting/blob/develop/include/c_common/points_input.h

We use Doxygen to generate the documentation
http://www.stack.nl/~dimitri/doxygen/

https://earthenginepartners.appspot.com/science-2013-global-forest

This step is often performed by users, but can be confusing. Create a "most common" path for importing in walk networks (perhaps from OSMnx) and support its conversion to peartree.

In #672 and #624, we discussed how the Steinhardt order parameter treats particles with zero neighbors. Steinhardt assigns a value of NaN. We need to check to see how other methods (Hexatic, Translational, SolidLiquid, LocalDescriptors) handle cases with zero neighbors.

The follow-up PR would basically be to review freud for other methods where this problem could arise and copy over the tes