Document r.and/r.or in the python and ruby api documentation

See issue rethinkdb/rethinkdb#1582 for discussion.

In the python client, r.and_ and r.or_ were added.  In addition, r.and and r.or in the ruby client were undocumented.  These commits fix the documentation to be up-to-date.  Section headings for '&' and '|' have been changed to be '&, and' and '|, or', and more syntax/examples were added to show valid usage.

In addition, the python `or.md` file suffered from some copy/paste problems that have been fixed.