Fix GitHub Pages deployment

[JohnTitor]

Currently GH Pages deployment fails:

 Warning: Uploaded artifact size of 2294743040 bytes exceeds the allowed size of 1 GB. Deployment might fail.

I guess the cause is we have too many targets, maybe reducing targets would be required (or, optimizing dox.sh?).

[JohnTitor]

Or, we could just stop using GitHub Pages in favor of docs.rs which now hosts the most (all?) supported targets.