Handle media types application/yaml and application/json

[jayvdb]

Fixes #41

[codecov]

Codecov Report

Merging #42 into master will decrease coverage by 0.16%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
- Coverage   95.21%   95.04%   -0.17%     
==========================================
  Files          36       36              
  Lines        1942     1957      +15     
==========================================
+ Hits         1849     1860      +11     
- Misses         93       97       +4     

Impacted Files	Coverage Δ
drf_spectacular/renderers.py	82.60% <75.00%> (-17.40%)	⬇️
drf_spectacular/views.py	96.55% <100.00%> (ø)

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[jayvdb]

I am not real sure about the best way to do the second commit adding two classes for the two extra mime types. I expect there should be a better way.

[jayvdb]

So 266904c1d0 is using the exact same approach as my commit in this PR; a bit neater of course.

[tfranzel]

superseded by 5f4fa7d and 266904c