Make source_dir = "module root folder" possible

[paulquiring]

It is to restrictive to force users to put all documentation into the root/docs folder. It is common practice to place the documentation next to the implementation. This is the idea behind the docs as code approach and allows to use the score process folder templates.

Using
docs( source_dir = ".", )
will cause the error
ERROR: Traceback (most recent call last): File "/home/qup6si/workspace/score/etas-eng/vsps_flatbuffers/BUILD", line 19, column 5, in <toplevel> docs( File "/home/qup6si/.cache/bazel/_bazel_qup6si/b3c8715a82908388a09c6520fc5950f3/external/score_docs_as_code+/docs.bzl", line 123, column 27, in docs srcs = native.glob([ Error in glob: invalid glob pattern './**/*.png': segment '.' not permitted WARNING: Target pattern parsing failed.

note entry index.rst and conf.py have been moved to the root folder.

[a-zw]

Since I don't think managing lists exclude filters is a good idea, here is an alternative idea which allows documentation in any folder of the repo: #431