Preserve field names when no formatting is configured

[sliverc]

Fixes #899

Description of the Change

This way it is possible to have field names which do not follow the python underscore convention. As this introduces new utilities took the opportunity to make format methods more consistent.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #909 (c6931ef) into master (a25e387) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #909      +/-   ##
==========================================
- Coverage   97.67%   97.67%   -0.01%     
==========================================
  Files          58       58              
  Lines        3102     3093       -9     
==========================================
- Hits         3030     3021       -9     
  Misses         72       72              

Impacted Files	Coverage Δ
rest_framework_json_api/django_filters/backends.py	100.00% <100.00%> (ø)
rest_framework_json_api/filters.py	100.00% <100.00%> (ø)
rest_framework_json_api/metadata.py	91.66% <100.00%> (ø)
rest_framework_json_api/parsers.py	98.55% <100.00%> (-0.17%)	⬇️
tests/test_views.py	100.00% <100.00%> (ø)

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[sliverc]

@n2ygk Do you think you will find time to have a look at this? Thanks.

[n2ygk]

@n2ygk Do you think you will find time to have a look at this? Thanks.

Sorry - I am so oversubscribed to github notifications that I miss the actionable ones like this. Looking at it now.

[n2ygk]

Nice cleanup!