om: improve handling of new lines

- create state diagram to model the state machine used by the stream
- add a way of switching off blank lines management in negative scope
  indenter
- ignore management of blank lines if its the first thing we see
- move non-generatable diagrams into doc/misc, they were just
  cluttering the diagrams directory
- change all om's specs to use a filtered ostream instead of a plain
  ostream, or else management of blank lines would be a no-op.