Mixedvines

Refactor distribution selection.
Fix get_all_params NumPy compatibility.
Improve stability of nbinom moment matching fit.
Move VineLayer out of the MixedVine scope and change private modifiers.
Refactor _VineLayer density methods.
Refactor marginal and copula setters.
Add Read the Docs configuration file.
Use numpydoc for documentation.

Use more list comprehensions and clarify checks.
Restructure package directories.
Change build system to flit.
Change license from GPLv3+ to GPLv3.
Clean up Sphinx configuration.
Remove duplicate method descriptions.
Limit length of docstring lines to 75 characters.
Improve return style.
Add documentation for exceptions.

Code and comments clean-up.
Use Structural Pattern Matching.

Update Docstrings for PEP 257.

Introduce random_state arguments.
Drop support for Python 3.3.x and lower.

Fix trunc_level parameter.
Fix pylint issues.
Add missing long_description_content_type to setup.