Implemented mimetype validator and checker.

[insightindustry]

Closes #63 . Added a MIME type validator and checker.

[codecov]

Codecov Report

Merging #66 into develop will decrease coverage by 0.28%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop      #66      +/-   ##
===========================================
- Coverage    83.87%   83.58%   -0.29%     
===========================================
  Files            4        4              
  Lines         1414     1438      +24     
  Branches       338      343       +5     
===========================================
+ Hits          1186     1202      +16     
- Misses         141      145       +4     
- Partials        87       91       +4     

Impacted Files	Coverage Δ
validator_collection/validators.py	85.72% <57.14%> (-0.44%)	⬇️
validator_collection/checkers.py	74.62% <75.00%> (+<0.01%)	⬆️
validator_collection/errors.py	100.00% <100.00%> (ø)

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