Squashed 'lectures/' changes from 8968d42..7306843 ...

7306843 Merged in changes that were inadvertently made in a subtree clone.
ed89997 Added \alertbf and Mark George’s text highlighting macros.

git-subtree-dir: lectures
git-subtree-split: 7306843

Squashed 'lectures/' content from commit 2b1085b ...

git-subtree-dir: lectures
git-subtree-split: 2b1085b