Introduce asset endpoints

[vkostyukov]

Turns out after we deprecated Twitter Futures in the mapper it became problematic to serve static files (although people generally not supposed to do that) with Readers.

This PR leverages cats-effect Resource to read Java resources and serve them as a static content.

An example:

Bootstrap
  .serve[Application.Javascript](Endpoint[IO].classpathAsset("/script.js"))

[codecov-io]

Codecov Report

Merging #1017 into master will increase coverage by 0.54%.
The diff coverage is 82.5%.

@@            Coverage Diff             @@
##           master    #1017      +/-   ##
==========================================
+ Coverage   84.28%   84.83%   +0.54%     
==========================================
  Files          48       49       +1     
  Lines         910      956      +46     
  Branches       57       67      +10     
==========================================
+ Hits          767      811      +44     
- Misses        143      145       +2

Impacted Files	Coverage Δ
core/src/main/scala/io/finch/Trace.scala	92.85% <100%> (+2.85%)	⬆️
core/src/main/scala/io/finch/EndpointModule.scala	83.01% <50%> (-2.7%)	⬇️
core/src/main/scala/io/finch/Endpoint.scala	72.89% <66.66%> (-0.66%)	⬇️
...re/src/main/scala/io/finch/endpoint/endpoint.scala	93.75% <93.75%> (ø)
core/src/main/scala/io/finch/Output.scala	95.65% <0%> (+0.78%)	⬆️
core/src/main/scala/io/finch/Input.scala	100% <0%> (+9.61%)	⬆️

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[rpless]

I like this. For the name, maybe classpathResource or resourceFromClasspath could work? I also like liftResource.

My only other thought is maybe we should replace the example of serving static files in the cookbook with this.

[vkostyukov]

I like this. For the name, maybe classpathResource or resourceFromClasspath could work? I also like liftResource.

My only other thought is maybe we should replace the example of serving static files in the cookbook with this.

Yes, I need to update the cookbook. Also I like your classpath idea.