Pass http content type header to body

[dxuhuang]

@benblack86 @amotamed @jlbelmonte @aliyakamercan @DanSimon

https://github.com/tumblr/colossus/issues/499

[codecov-io]

Codecov Report

Merging #534 into master will increase coverage by 0.1%. The diff coverage is 95.74%.

@@            Coverage Diff            @@
##           master     #534     +/-   ##
=========================================
+ Coverage   84.71%   84.82%   +0.1%     
=========================================
  Files          98       98             
  Lines        4293     4309     +16     
  Branches      331      343     +12     
=========================================
+ Hits         3637     3655     +18     
+ Misses        656      654      -2

Impacted Files	Coverage Δ
...a/colossus/protocols/http/HttpResponseParser.scala	72% <100%> (+8.84%)	:arrow_up:
...main/scala/colossus/protocols/http/HttpParse.scala	100% <100%> (+9.67%)	:arrow_up:
...la/colossus/protocols/http/HttpRequestParser.scala	95.65% <100%> (+0.91%)	:arrow_up:
...n/scala/colossus/protocols/http/HttpResponse.scala	88.88% <100%> (ø)	:arrow_up:
...rc/main/scala/colossus/protocols/http/Header.scala	83.85% <66.66%> (-0.53%)	:arrow_down:
.../main/scala/colossus/protocols/http/HttpBody.scala	79.16% <83.33%> (ø)	:arrow_up:

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[benblack86]

Code looks good, can we get some tests?

[dxuhuang]

bump