Add scala adapters for doOnEach operator.
Remove unnecessary cast.
Merge pull request #555 from Netflix/docs

skipUntil() marble diagram and wiki link in javadoc
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' into scala-do-operator
Remove unnecessary type parameter.

Apparently (to my surprise), the implicit conversions are smart enough
to resolve this.
Add type variances for doOnEach actions.

This fixes the use of contravariant actions.
Merge pull request #537 from landonf/scala-do-operator

Add scala adapters for doOnEach operator.
Merge pull request #560 from landonf/java-do-variances

Add type variances for doOnEach actions.