add gitignore file
update boot.py
add InputStream.__repr__
add a debug command to OMeta runtime
add the consumed_by operator
add a range operator, working with any datatype, even if the syntax only allow string for now
add the interleave operator

- adapt code from OMeta/JS
- add special treatment so that special behaviour with kleen-start and ?
  is kept when also using binding.
add xor operator
add the index consumed by operator
simplify parse trees for ometa grammars