Add FORD gh-pages

[zoziha]

• [x] Add doc-deployment CI;
• [x] Add fftpack_kind doc.

As @juannaviap in the forum asked about the use of fftpack. This PR will deploy fftpack's FORD documentation to the gh-pages branch.

The effect is as follows:

• fftpack's FORD
• Specs: The fftpack module