add answers for first two assignments

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

Prefer match statements to decompose lists:

```scala
  def combine(trees: List[CodeTree]): List[CodeTree] = 
    trees match {
      case left :: right :: tail =>
        Fork(left, right, chars(left) ++ chars(right), weight(left) + weight(right)) :: tail
      case _ => trees
    }
```

Also I've seen the more general collection `++` for concatination of lists more than the list specific `:::`, but I'm not sure that's just me or a general trend.