Add sbt-airframe plugin

[xerial]

• Support generating HTTP client code from airframe-http interfaces
• plugin settings
• Read http interfaces
• Generate http client code for JVM
• Generate Scala.js client code

[codecov]

Codecov Report

Merging #943 into master will increase coverage by 0.02%.
The diff coverage is 80.76%.

@@            Coverage Diff             @@
##           master     #943      +/-   ##
==========================================
+ Coverage   80.45%   80.48%   +0.02%     
==========================================
  Files         250      250              
  Lines        9472     9479       +7     
  Branches      641      647       +6     
==========================================
+ Hits         7621     7629       +8     
+ Misses       1851     1850       -1

Impacted Files	Coverage Δ
.../main/scala/wvlet/airframe/http/router/Route.scala	68.75% <ø> (ø)	⬆️
...rc/main/scala/wvlet/airframe/http/HttpClient.scala	97.14% <0%> (-2.86%)	⬇️
...tp/src/main/scala/wvlet/airframe/http/Router.scala	64.44% <100%> (ø)	⬆️
...log/jvm/src/main/scala/wvlet/log/io/Resource.scala	88.88% <100%> (+0.1%)	⬆️
...c/main/scala/wvlet/airframe/surface/Surfaces.scala	67.7% <100%> (+0.68%)	⬆️
...irframe/surface/reflect/ReflectMethodSurface.scala	80% <66.66%> (ø)	⬆️
...rframe/surface/reflect/ReflectSurfaceFactory.scala	90.44% <82.35%> (+0.44%)	⬆️
...shared/src/main/scala/wvlet/log/io/StopWatch.scala	80.2% <0%> (+0.2%)	⬆️
...irframe/src/main/scala/wvlet/airframe/Binder.scala	70% <0%> (+2.5%)	⬆️

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[xerial]

To support Scala.js code generation, we should make airframe-control / airframe-http cross projects for Scala JVM/Scala.js. I'll work on it in another PR.