Add shortcuts for local and lambda

[kaifee-haque]

Summary of Changes

• Shortcut for local definitions
• Shortcut for anonymous functions
  • full expression uses lambda as the character isn't supported by MarkUs yet
• else clause for cond expression is moved to its own line

[Raymo111]

I have shortcuts for lambda, I just haven't pushed them yet. Markus does support the greek character; I submitted my last assignment with it and it looks cleaner. I'd like to keep else on the same line because it's easier to hit enter than to deal with formatting. I might also implement another cond to check if something is empty and return empty (I'll call it bc for base case or something).

[Raymo111]

I'm closing this PR for now just because I've already implemented this; give me a week or two to merge them before adding anything else. Thanks for contributing!