[ENH] Add optional removal of accents on functions.clean_names, enabled by default.

[mralbu]

PR Description

Changes proposed in the pull request:

• add optional removal of accents on functions.clean_names, enabled by default.

Example API:

# create test DataFrame
df = pd.DataFrame({"João": [1, 2], "Лука́ся": [1, 2], "Käfer": [1, 2]})

# remove column name accents
df = df.clean_names(strip_accents=True)
expected_columns = ["joao", "лукася", "kafer"]
assert set(df.columns) == set(expected_columns)

This PR resolves #502

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Relevant Reviewers

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• @ericmjl

[codecov]

Codecov Report

Merging #506 into dev will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #506      +/-   ##
==========================================
+ Coverage   92.84%   92.88%   +0.04%     
==========================================
  Files           9        9              
  Lines         838      843       +5     
==========================================
+ Hits          778      783       +5     
  Misses         60       60

[ericmjl]

Superb, thanks @mralbu!