Reorganize files
Fix broken links
Correct mistake in the specification for Problem 1 in Hoomework 2
lecture notes
Do not print quotes for symbols in error message
Edit a bit
Add sheet for Exercise 3
Finish the sheet for Homework 3
Fix typo; improve text
Refine problems
Put sample solutions online
Add a README.md
Update READEME.md
Update README.md again
Define hard deadline and soft deadline
Fix the return type for `eval`
Refine problem specification
Add a missing case class for `Value`
Rename a constructor
Fix broken links