Fix typos in lecture 01

Someone doesn't know how to spell.
Maybe it's @mitio...
Remove an exclamation mark

Apparently we shouldn't be exited.
Add lecture 03
Fixed style error

Using unless with else where the style guide states that we should not.
Separate heading and subheading on slide 30
Typo
Fix examples in lecture 03
Correct spelling mistakes
Fix lambda call according to style guide
Correct method name
Fix small inaccuracies
Fix 4 typos

I checked the slides and found 4 different small typos.
Fix 5 typos
Lecture 04
Fix some typos
Fix indentation and typo
Fix 2 typos
Replace albino with pygments.rb

Albino seems to be deprecated in favor of pygments.rb. The latter is
also faster than albino–on my machine that's nearly twice as fast.
Lecture 05
Fix small typos