Deprecate obsolete reactive API, improve existing Reactive documentation

    * Remove obsolete rx-example module
    * Properly document interoperability with Reactor context
    * Update reactive readme
diff --git a/build.gradle b/build.gradle
index 4fe2225..d5ed5b9 100644
--- a/build.gradle
+++ b/build.gradle
@@ -11,7 +11,7 @@
 def sourceless = ['kotlinx.coroutines', 'site', 'kotlinx-coroutines-bom']
 def internal = ['kotlinx.coroutines', 'site', 'benchmarks', 'knit', 'js-stub', 'stdlib-stubs', 'binary-compatibility-validator']
 // Not published
-def unpublished = internal + ['kotlinx-coroutines-rx-example', 'example-frontend-js', 'android-unit-tests']
+def unpublished = internal + ['example-frontend-js', 'android-unit-tests']
 
 static def platformOf(project) {
     def name = project.name