Fix dead links in documentation

[ghost]

There are many dead links in the documentation. I first replaced them by looking for the original or similar source. For example, for the dead Adobe links, I instead linked to the MSFT typography docs, which had similar information. When this approach didn't work, i used an archive link instead.

[jtanx]

Needs to be fixed in source https://github.com/fontforge/fontforge/tree/master/doc/sphinx