Add headerNotParse function to Rs

[jsancio]

ran sbt -J-XX:MaxMetaspaceSize=1G test.

[jsancio]

Resolves #929 .

[codecov-io]

Codecov Report

Merging #930 into master will decrease coverage by 0.62%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #930      +/-   ##
==========================================
- Coverage   82.81%   82.18%   -0.63%     
==========================================
  Files          51       51              
  Lines         768      769       +1     
  Branches       39       34       -5     
==========================================
- Hits          636      632       -4     
- Misses        132      137       +5

Impacted Files	Coverage Δ
core/src/main/scala/io/finch/endpoint/header.scala	62.5% <100%> (ø)	⬆️
core/src/main/scala/io/finch/internal/Rs.scala	100% <100%> (ø)	⬆️
core/src/main/scala/io/finch/Input.scala	87.5% <0%> (-12.5%)	⬇️

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[vkostyukov]

Nice @jsancio! I will release 0.18.1 shortly.