Docs: Use Read the Docs SPHINXOPTS

`-W --keep-going` will build everything but raise an error on any warnings.  Should mean that github actions will correctly flag a failure when attempting to build docs.  Including this current commit until the `internal_stats` command gets a help message.

docs/Makefile

@@ -2,7 +2,7 @@
 #
 
 # You can set these variables from the command line.
-SPHINXOPTS    =
+SPHINXOPTS    = -W --keep-going
 SPHINXBUILD   = sphinx-build
 PAPER         =
 BUILDDIR      = build