[WIP] change the relative location of the filename for source code lookup. Fixes #2126

[adam-kerrigan]

Summary

• Generation of links to source code in the pymatgen.core have been fixed.
• Generation of links to source code where the line numbers cannot be found have been fixed.

This fixes #2126. I was unsure on the difference between conf-docset.py, conf-normal.py and conf.py so I only updated the ones with the linkcode_resolve function in.

TODO (if any)

Generation of the Documentation, I couldn't find a guide to building the documentation and when I do I get far more changes than I expect as well as 608 warnings from sphinx some of which are listed below:

• Adds '()' to end of property names in genindex.html
• Adds a space to the end of the meta tags
• Removes alt="Documentation Home" from every page.

Also I have noticed that the documentation for BoltzTraP2 is missing on the doc site however when I build it is present.

Before a pull request can be merged, the following items must be checked:

• Code is in the standard Python style. The easiest way to handle this
  is to run the following in the correct sequence on your local machine. Start with running
  black on your new code. This will automatically reformat
  your code to PEP8 conventions and removes most issues. Then run
  pycodestyle, followed by
  flake8.
• Docstrings have been added in the Google docstring format.
  Run pydocstyle on your code.
• Type annotations are highly encouraged. Run mypy to type check your code.
• Tests have been added for any new functionality or bug fixes.
• All linting and tests pass.

[shyuep]

Thanks.

[coveralls]

Coverage decreased (-0.6%) to 83.013% when pulling e2158fc on adam-kerrigan:doc_conf into cb9854d on materialsproject:master.