Deprecate kikuchipy.pattern.correlate module

[hakonanes]

Description of the change

• Deprecate kikuchipy.pattern.correlate module, to be removed in v0.5. Use kikuchipy.indexing.similarity_metrics instead.

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

Minimal example of the bug fix or new feature

>>> import kikuchipy as kp
>>> s = kp.data.nickel_ebsd_small()
>>> p1 = s.inav[0, 0].data
>>> p2 = s.inav[0, 1].data
>>> print(kp.pattern.correlate.normalized_correlation_coefficient(p1, p2))
0.9974703
/home/hakon/kode/kikuchipy/kikuchipy/pattern/correlate.py:32: VisibleDeprecationWarning: Function `normalized_correlation_coefficient()` is deprecated and will be removed in version 0.5. Use `kikuchipy.indexing.similarity_metrics.ncc()` instead.
  since="0.4",
>>> print(kp.indexing.similarity_metrics.ncc(p1, p2))
0.99747044

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the
  unreleased section in doc/changelog.rst.

[hakonanes]

Will merge after checks pass.