Schematics-xml

- Ensure that lists with `None` value aren't turned into `[None]` (7)

- Allow user to set XML encoding (6)
- Added encoding parameter to to_xml
- Changed default encoding to UTF-8.
- Added XMLModel attribute xml_encoding with default 'UTF-8'.
- Added docs detailing how to set the encoding.
- Ensure deeply nested lists are traversed even if the parent is OK. (5)
- Test schematics serialized_name BaseType feature.

- Support lists with a single item in XML being converted to raw_data with a list not dict. (2)
- Set reports no in pylintrc (1)
- Removed keyword only args from to_xml function for py 3.3/3.4 support. (3)

- Fixed travis YAML file parse error
- Allow travis failures for pypy and pypy3
- Added pytest-cov
- Fixed pylint issue with __init__ import
- Cleaned up test requirements

- Initial release