DOC: Add `readthedocs` documentation site infrastructure

[jhlegarreta]

DOC: Add readthedocs documentation site infrastructure

Add readthedocs documentation site configuration and site index files. Add the necessary packages to generate the documentation from the source files, including Python module methods, and script arguments.

Add Makefile and make.bat files to build the documentation locally.

Add the reference to the readthedocs website and the corresponding build badge to the README file.

[jhlegarreta]

This supersedes the gh-pages branch.

[jhlegarreta]

This fixes the readthedocs build failure concerning the absence of the corresponding config files: https://readthedocs.org/projects/whitematteranalysis/builds/22133730/

[jhlegarreta]

readthedocs build is passing; test, package build failures are unrelated to this patch set.