Adds default configuration for PDF generation

[SecondSkoll]

Adds files required for PDF generation, including some base images, fonts.
Adds make targets to generate PDFs, including a separate target to install local packages.
Provides configuration for the PDF in custom_conf.
Adds CSS role to allow HTML heading on index without affecting PDF generation due to nesting issue.

[ru-fu]

I haven't tested it yet, but overall this looks good!
Some comments about keeping the implementation clean and maintainable.

[ru-fu]

Blocking because we cannot remove the _build folder (that has our HTML output).

Requested changes have been made

[ru-fu]

A couple more small comments, but overall, this looks good!

Now the next question is - will RTD pick up this PDF build automatically, or does it need some configuration (probably in .readthedocs.yaml)?

[SecondSkoll]

@ru-fu As long as the .readthedocs.yaml file has PDF listed under formats - as the Stater Pack does by default - the configuration will be picked up.

[ru-fu]

Thanks! :)

[ru-fu]

@ru-fu As long as the .readthedocs.yaml file has PDF listed under formats - as the Stater Pack does by default - the configuration will be picked up.

Curious how the installation of packages works there ... do they have them installed already? Or where do they get them from?

[SecondSkoll]

@ru-fu I imagine they have set build systems with something like Bamboo, rather than ad-hoc or request driven environments. From the lack of xindy support I assume they don't try to dig through configs or anything super clever.