compiler: add `else' support in `try'

This is a bit tricky, since we'll also have to support `finally' in the end, 
I've introduced an Else statement on my own to be able to recognize it.

In the end, we even do a better job than Python (sort of) since we support a 
syntax that doesn't in Python:

  (try
   (pass)
   (else (pass))

is translated to:

  try:
     pass
 else:
    pass

Which seems impossible in Python syntax. How fun?

This fixes issue #74.