Expand cheatsheet

[harsh183]

• [ ] Basic Testing
• [x] Inheritance
• [ ] Generic classes (plus some fancy stuff from here)
• [x] Functions within classes
• [x] Collections
• [x] Boolean expressions with Ranges
• [ ] Coroutine related

Note: It's probably a good idea to fix up the lesson pages on the side of things as well. The cheat sheet and lessons go hand in hand.