Add pre-commit checks and various other cleanup & fixes

[desilinguist]

This PR closes #110.

Apply pre-commit checks to all files.

• Add pre-commit configuration and dependency.
• Add newlines to end of files.
• Remove unnecessary whitespace.
• Make author information current in docstrings.
• Update all docstrings to be pep257-compliant, where possible.
• Add noqa directives where necessary.
• Improve type type information in docstrings.
• Use double backticks consistently in docstrings.
• Fix typos in README.
• Add plugin configuration files.
• Add pre-commit badge and add alt text everywhere.

Replace deprecated pandas.util.testing.

• Use appropriate replacements from numpy and nose.

Update setup.py

• Add maintainer name and email.
• Update Jeremy's email.
• Add Python 3.10 as supported version.
• Update description.

Fix various issues in documentation.

• Update version in conf.py.
• Fix typos.
• Create links for modules, classes, and methods.
• Update requirements.
• Specify language.
• Fix issues in docstrings for sphinx.

[codecov]

Codecov Report

Base: 94.32% // Head: 94.22% // Decreases project coverage by -0.09% ⚠️

Coverage data is based on head (1516070) compared to base (b5e41d3).
Patch coverage: 93.33% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
- Coverage   94.32%   94.22%   -0.10%     
==========================================
  Files           7        7              
  Lines        1004     1004              
==========================================
- Hits          947      946       -1     
- Misses         57       58       +1     

Impacted Files	Coverage Δ
setup.py	0.00% <0.00%> (ø)
factor_analyzer/factor_analyzer.py	94.80% <85.71%> (ø)
factor_analyzer/utils.py	89.05% <92.85%> (ø)
factor_analyzer/rotator.py	95.63% <98.33%> (ø)
factor_analyzer/confirmatory_factor_analyzer.py	97.02% <98.46%> (ø)
factor_analyzer/__init__.py	100.00% <100.00%> (ø)
factor_analyzer/test_utils.py	98.42% <100.00%> (ø)

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[desilinguist]

I think the change in coverage is acceptable given that the number of lines went up because of applying black and expanding the docstrings. I didn't really change any code.

[jbiggsets]

This looks good to me!