Round 1 of standardizing DPF-Core doc

[PipKat]

No description provided.

[PipKat]

@RobPasMue I meant to start with DPF-Post doc but accidentally started with DFP core. This doesn't address Vale stuff but just tries to reorganize the doc content to be more like other repos. They use a "docs" directory rather than a "doc" directory. Should this be changed for consistency sake? When I changed the name of the "APIs" section to "API reference", a local doc generation didn't show the APIs. Is this expected? I didn't submit a change to the api/index.rst file, just in case it would mess up the doc for this section. Based on the number of failed checks on PRs for this repo, I don't expect the checks for this PR to pass either. However, I wanted to submit the changes I've made so far before switching to DPF-Post doc.

[codecov]

Codecov Report

Merging #426 (d3afebe) into master (c55a98e) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #426      +/-   ##
==========================================
- Coverage   86.39%   86.36%   -0.03%     
==========================================
  Files          61       61              
  Lines        6717     6717              
==========================================
- Hits         5803     5801       -2     
- Misses        914      916       +2     

[RobPasMue]

LGTM! It's a good restructuring of the docs. Thanks @PipKat.

[PProfizi]

@PipKat I've realized there is a problem with doc generation, going back a few days actually. I have to investigate but in the meantime I'd rather not merge a PR concerning the doc.
If you do not mind maybe PyDPF-Post would be a better candidate. We will try not to merge anything here until this issue is resolved.