Ruyaml

- fix Text not available on 3.5.0 and 3.5.1 (reported by Charles Bouchard-Légaré)

- updates for mypy --strict
- preparation for moving away from inheritance in Loader and Dumper, calls from e.g.
the Representer to the Serializer.serialize() are now done via the attribute
.serializer.serialize(). Usage of .serialize() outside of Serializer will be
deprecated soon
- some extra tests on main.py functions

- fix for issue 97, clipped block scalar followed by empty lines and comment
would result in two CommentTokens of which the first was dropped.
(reported by Colm O'Connor)

- fix for issue 96, prevent insertion of extra empty line if indented mapping entries
are separated by an empty line (reported by Derrick Sawyer)

- allow ':' in flow style scalars if not followed by space. Also don't
quote such scalar as this is no longer necessary.
- add python 3.6 manylinux wheel to PyPI

- fix for issue 93, insert spurious blank line before single line comment
between indented sequence elements (reported by Alex)