Use standard x, y axis order if we do not know better
Add Insert, Update and Delete writers

This change also adds some type annotations for better type
checking, introduces different write options for writing
transactions and queries, and provides new writeGetFeature and
writeTransaction methods.
Export getParser()

This reduces the API footprint of versioned parsers, because
only the base parser needs to be exported as symbol, and
versioned parsers can be accessed using the getParser() method.
Export the WFS parser and its write methods

For using the WFS parser, users need to be able to write
GetFeature queries and transactions.
No native element on GetFeature queries
Addressing review comments

* Do not write xmlns
* Make @this annotations consistent
* Handle numbers and strings for attribute values
* Fix defaultNamespaceURI scope
Merge pull request #1339 from ahocevar/wfs-transaction

Transaction handling and exports for the WFS parser