Replace PR #48: FORD commits only

[rouson]

As requested in an issue comment, this PR contains only commits related to adding FORD documentation. The text below is mostly copied from the now-closed PR #48, which the current PR replaces.

---

1. Add a top-level doc-generator.md FORD project file that produces HTML documentation inside doc/html/ and includes the top-level README.md content in the landing page: doc/html/index.html.
2. Replaces ! with !! in comments only in the nf_random_mod just after the first line of the module and just after the first lines of the procedure interface bodies. Doing so triggers for to include the corresponding comments in the generated documentation.
3. Add the doc/ subdirectory to the .gitignore file.

If this PR gets merged, then executing

cd neural-fortran
ford doc-generator.md

will produce an uncompressed version of doc.tar.gz.

If approved, this PR can be updated to apply similar changes to the rest of the files in src/:

• [x] mod_activation.f90

• [x] mod_mnist.f90

• [x] mod_parallel.f90

• [x] mod_layer.f90

• [x] mod_network.f90

[rouson]

@milancurcic this PR is now ready to merge. The documentation now contains lots of text from the comments in the code. See doc.tar.gz.

[rouson]

@milancurcic it appears that I don't have the privileges required to merge this PR.

[milancurcic]

OK, can you try now?

[rouson]

Yes, done. Thanks!