Polish and cont'd.
\aold & \apred are commands, no longer definitions
Update labels and build minitoc.
Create empty sections to get labels.
Add the section about expressions.
Add the `bigpre` environment.
Add the `em` and `strong` command.
Use `\strong` instead of `\tb`.
Support multi-languages.
Use `paralist`.
Cont'd.
Use the `bigpre` environment.
Update `\circled` style.
Update `\circled`.
Polish.
Polish.