Make python examples PEP8 compliant.

These are my proposed fixes for rethinkdb/rethinkdb#2534.
Can you put a newline before the `.` in Python?

IMO the "dots on a new line" format works really well for small filters etc., and the "newline after opening paren" format works really well for larger filter expressions that don't fit on one line.  (The dots on the new line remind me a lot of bash pipes, actually, which may be why I like them.)