add uri model

[pepegar]

Introduces a Uri class that will be used on the high level API.

Waiting for atto to be cross-compiled to ScalaJS, since we're using at our very core right now. Done now :)

TODO:

• tests for toString (will be used to translate to the raw string that the low level uses.
• integrate on hi

closes #26

[codecov]

Codecov Report

Merging #29 into master will decrease coverage by 0.32%.
The diff coverage is 70.51%.

@@            Coverage Diff             @@
##           master      #29      +/-   ##
==========================================
- Coverage   82.49%   82.16%   -0.33%     
==========================================
  Files          15       16       +1     
  Lines         297      314      +17     
  Branches        2        4       +2     
==========================================
+ Hits          245      258      +13     
- Misses         52       56       +4

Impacted Files	Coverage Δ
core/shared/src/main/scala/hammock/hi/dsl.scala	37.5% <ø> (+1.13%)	⬆️
.../src/main/scala/hammock/jvm/free/Interpreter.scala	90.47% <100%> (ø)	⬆️
core/shared/src/main/scala/hammock/hi/Opts.scala	71.42% <33.33%> (ø)	⬆️
...e/shared/src/main/scala/hammock/free/algebra.scala	44.44% <50%> (ø)	⬆️
core/shared/src/main/scala/hammock/Hammock.scala	72% <69.56%> (-0.42%)	⬇️
core/shared/src/main/scala/hammock/Uri.scala	70.83% <70.83%> (ø)

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