Created section on useful package: removed `enumitem` because it doesn't work
with beamer `itemize`.

Moved all the basic items to `basics.tex` and then include it later. This also
speeds up compiling slightly.

Advanced Math is mostly just how to use `amsmath` and based on common mistakes
I've seen other people make.

Defining Your Own... was separated into sections: Commands,
Environments, a short note on theorems, and packages/document classes. Packages
are really just less specific document classes.

Slightly changed `lug.cls` to better fit on the page, while still being
accurate.

Added essential resources and whitespace sections.

Added a few citation pitfalls.