Update to better checkstyle

Upgrade to RxJava 3.0.6, release 3.0.1

Merge branch '3.x' of https://github.com/akarnokd/RxJavaExtensions.git …

…into 3.x

Upgrade to RxJava 3.0.0-RC8

Upgrade to RxJava 3.0.0-RC6

Upgrade 3.0.0-RC5

Upgrade to RxJava 3.0.0-RC4

Upgrade to RxJava 3.0.0-RC3, adjust internals

Fix javadoc links

Merge branch '3.x' of https://github.com/akarnokd/RxJavaExtensions.git …

…into 3.x