Dicomweb-client

Refactoring

* Drop support for Python2 due, since Python 2.7 will not be maintained beyond January 1st 2020
* Add type hints

Enhancements

* Remove quotes from `boundary` in the content type header field of multipart related messages. Note: While the quotes were standard-compliant, some origin servers didn't handle them correctly.
* Accept `"application/dicom+json"` as well as `"application/json"` for query and retrieve metadata methods to improve backwards compatibility with older origin servers that implemented earlier versions of the DICOMweb standard.
* Improve type hints in method docstrings
* Update dependencies for running continuous integration tests
* Run test cases with additional Python 3 versions

Bug fixes

* Fix return value of `retrieve_instance_metadata()`: return single dictionary instead of list of dictionaries

Features

* add support for authentication based on [requests authentication objects](http://docs.python-requests.org/en/master/user/authentication/)

New features
* add new API methods for WADO-RS Retrieve Rendered Transaction
* add ``media_types`` parameter to WADO-RS methods to enable specification of acceptable media type ranges

API changes
* remove parameter ``image_format`` and add parameter ``media_types`` to ``retrieve_instance_frames()`` method

Bug fixes

Fix parsing of data elements of DICOM JSON encoded data sets that have value representation PN and an empty value