Replace Codec requirement by an Encoder requirement

[BenFradet]

I didn't understand why requests with body needed a whole Codec so I replaced it with only Encoder.

[codecov]

Codecov Report

Merging #107 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #107   +/-   ##
=======================================
  Coverage   69.26%   69.26%           
=======================================
  Files          22       22           
  Lines         615      615           
  Branches        6        6           
=======================================
  Hits          426      426           
  Misses        189      189

Impacted Files	Coverage Δ
core/shared/src/main/scala/hammock/Hammock.scala	72% <ø> (ø)	⬆️

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[pepegar]

Heya @BenFradet! Thanks for this!

Currently I'm away from a computer but will get to review this on Monday. Sorry for the delay!

Cheers!

[pepegar]

LGTM, thanks for this @BenFradet !