Add contrib ff descriptor

[TsumiNa]

New features

• Add Mordred descriptor calculator.
• Extended FrozenFeaturizer descriptor.

Improve docs

• Add extra information for parameter n_jobs: int to warning users when setting this parameter to 0.

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (develop@ba633c0). Click here to learn what that means. The diff coverage is 86.51%.

@@            Coverage Diff             @@
##             develop     #125   +/-   ##
==========================================
  Coverage           ?   82.34%           
==========================================
  Files              ?       68           
  Lines              ?     4430           
  Branches           ?        0           
==========================================
  Hits               ?     3648           
  Misses             ?      782           
  Partials           ?        0

Impacted Files	Coverage Δ
xenonpy/contrib/foo/descriptor/foo.py	100% <ø> (ø)
xenonpy/descriptor/frozen_featurizer.py	89.13% <100%> (ø)
xenonpy/descriptor/fingerprint.py	96.38% <100%> (ø)
xenonpy/descriptor/compositions.py	98.93% <100%> (ø)
xenonpy/descriptor/structure.py	46.66% <100%> (ø)
.../contrib/extend_descriptors/descriptor/__init__.py	100% <100%> (ø)
xenonpy/contrib/foo/descriptor/__init__.py	100% <100%> (ø)
...riptors/descriptor/frozen_featurizer_descriptor.py	43.75% <43.75%> (ø)
tests/foo/descriptor/test_foo.py	83.33% <75%> (ø)
...xtend_descriptors/descriptor/mordred_descriptor.py	95.65% <95.65%> (ø)
... and 1 more

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