If 'data' and 'params' in opts, don't overwrite 'data'.

This allows users to explicitly pass 'data' and 'params' together.

Addresses cloudant-labs/cloudant-python#45
Add unit test for testing multi-key view query.

Tests POST to view functionality.
Merge pull request #46 from mgmarino/fix_view_post

Remove special handling of post/put in _make_request.