Add kategory-effects-rx2

[pakoito]

Depends on #232

This PR adds support for RxJava 2's Observable. It's a WIP until I figure some things out, like whether we need to support Single, if tailrecM is correct as it's slow as fuck, and whether to provide a better DSL for binding w/ Schedulers.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@e3256e1). Click here to learn what that means.
The diff coverage is 89.06%.

@@            Coverage Diff            @@
##             master     #233   +/-   ##
=========================================
  Coverage          ?   43.11%           
  Complexity        ?      323           
=========================================
  Files             ?      150           
  Lines             ?     4010           
  Branches          ?      402           
=========================================
  Hits              ?     1729           
  Misses            ?     2160           
  Partials          ?      121

Impacted Files	Coverage Δ	Complexity Δ
kategory-core/src/main/kotlin/kategory/data/Try.kt	20.72% <ø> (ø)	5 <0> (?)
...re/src/main/kotlin/kategory/typeclasses/Comonad.kt	65% <ø> (ø)	0 <0> (?)
...core/src/main/kotlin/kategory/typeclasses/Monad.kt	72.54% <100%> (ø)	0 <0> (?)
...src/main/kotlin/kategory/typeclasses/MonadError.kt	69.23% <100%> (ø)	0 <0> (?)
...kategory/effects/instances/ObservableWInstances.kt	88.23% <88.23%> (ø)	0 <0> (?)
...c/main/kotlin/kategory/effects/data/ObservableW.kt	88.46% <88.46%> (ø)	6 <6> (?)

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[pakoito]

Threading and Schedulers should be a parameter

[pakoito]

Proposed API:

ObservableWFlatMapInstances.binding {
 val users = getUserList().bind(destination = Schedulers.newThread())
 val user = Observable.from(users).bind()
 val friends = getFriends(user.id).bind(destination = Schedulers.newThread())
 val result = updateInDatabase().bind(origin = DatabaseScheduler.instance())
 yield(result)
}

[pakoito]

Ready for release @kategory/maintainers !!

[nomisRev]

This has moved to root build.gradle while ago