add answers for first two assignments

i just add my answers on my repo. this include solutions for first two assignments with example assignment

Just formatting, but it's weird to have `{ }` brackets around one and not the other. I'd probably write it as:

```scala 
  def until(isDone: List[CodeTree] => Boolean, makeTree: List[CodeTree] => List[CodeTree])(tree: List[CodeTree]): List[CodeTree] =
    if (isDone(tree)) tree
    else until(isDone, makeTree)(makeTree(tree))
```