add missing public items to __all__

Added a few more public classes, and sorted the __all__ value.
The Attribute and Parameter classes are not included as they can
be imported from the `mwparserfromhell.nodes.extras` without
linter complaining.  They could be added to this __all__ too.

fix example: wrap dict.values in list()

In Python 3, `dict.values` returns a dict_values object, which does not support indexing.

Drop support for EOL Python 2.6, 3.2 and 3.3

Add <wbr> to definitions.py

Added to MediaWiki in ff74113bea (T54468).