Pyxnat

Improvements
* Replace nose with `pytest` as testing framework (167)
* Include `digest` as File class attribute (169)
* Support for Python release 3.7 terminated due to its end-of-life
* Official support added for Python release 3.9

Bug fixes
* Correct the list of available attributes for Resource class
* `bin/sessionmirror.py`: fix resource cache directory path composition
* PyMuPDF `Pixmap` class methods renamed (https://github.com/pymupdf/PyMuPDF/issues/1041)
* Refactor CI tests as some Central XNAT public resources are gone (further actions might be required in a future, see 173)

New Features
* Main functionalities for running and monitoring XNAT pipelines.
* XNAT Data Sharing features available for Subject and Experiment resources

Improvements
* Automated CI pipeline ported to GitHub-Actions. Travis integration is no longer working.
* Split CI pipeline in two different and independent workflows, `ci.yml` and `docs.yml`
* Support for Python releases 2.7 and 3.6 terminated due to its end-of-life.
* Official support added for Python release 3.8

Bug fixes
* `xnat-docker-compose` pinned to tag 1.8.1 due to CI-related errors (workaround fix)
* `xpass.py`: fix credentials parsing for `.xnatPass` configuration file
* `bin/sessionmirror.py`: fix PET experiments mirroring
* minor fix to `pipeline.status()` function
* various style improvements (PEP 8)

Now includes improved representation of objects such as `Project`, `Subject`, `Experiment`, `Scan` and `Resource`.


Experiments defined with `project_id` and `experiment_id` (without subject level) are automatically assigned with a three-level URI (completed with `subject_id`). Avoids some issues with some requests and improves execution speed.

Docker-based tests are back and operational.

Minor changes:
- added `Project.description()`
- various bugfixes and style improvements

Minor release with some bugfixes/cleaning.

Docker-based tests are removed until we find why they fail on Travis CI.

CI tests are now distributed along with the PyPI package.

* New Features:
- CI tests can be skipped if no network connectivity or no Docker-based XNAT available
- bin/sessionmirror.py: migrate an experiment between two XNAT instances

* Improvements:
- More tests
- Refreshing documentation

* Bug fixes:
- XNAT REST API compatibility (`Interfaces.version()`, `Schemas`, etc)
- Removed deprecated references to cache support
- Python 3 fixes

* Improvements
- Refreshing documentation
* Bug fixes
- If verify not defined, don't store it
- Closing requests session on disconnection