Update tables and headings formatting.

commit 4ab3ff82
Author: Jason Kridner <jkridner@beagleboard.org>
Date:   Tue Oct 25 21:38:16 2022 -0400

    More spelling fixes

commit fce576ba
Author: Jason Kridner <jkridner@beagleboard.org>
Date:   Tue Oct 25 13:52:28 2022 -0400

    Fixed a bunch of spelling and linking errors

commit 185218ee
Merge: 39c2dd78 c3b7fb7f
Author: Jason Kridner <jkridner@beagleboard.org>
Date:   Mon Oct 24 13:58:46 2022 -0400

    Merge branch 'main' of git.beagleboard.org:docs/docs.beagleboard.io

commit 39c2dd78
Author: Jason Kridner <jkridner@beagleboard.org>
Date:   Mon Oct 24 13:54:54 2022 -0400

    books/pru-cookbook/code: fix some spelling issues

commit c3de7ef6
Author: Jason Kridner <jkridner@beagleboard.org>
Date:   Mon Oct 24 13:44:15 2022 -0400

    books/pru-cookbook: fix references to code

commit c4a51c22
Author: Jason Kridner <jkridner@beagleboard.org>
Date:   Mon Oct 24 12:18:03 2022 -0400

    books/pru-cookbook: move code to submodule

Original from benedict.hewson (https://forum.beagleboard.org/t/bbai-64-pinmux-spreedsheet/32418/6)