Add first slides of the 1-intro lecture
Add the slides up to loop/recur
Fix lecture name

01-intro is a better name than 1-intro, because lexicographically it
comes after 11-something.
Oops. Did a half-ass job of renaming the lecture file
Add few more slides
Pinking shears

Since the parser is fixed we don't need the trailing
whitespace anymore.
Make it a proper predicate-looking function
Add recur/loop slides
Use annotations in lecture 1
Force all pow arguments to bigint

Otherwise it inconsistently throws integer overflow
errors, instead of stack overflows.