add Scala 3.0.0 to crossbuild (and drop -RC2) (scala#229)

backpublish 1.0.0-RC1 for Scala 3.0.0-RC3

Merge pull request scala#216 from SethTisue/scala-3.0.0-RC2

Merge pull request scala#150 from scala/2.13

Adapt to 2.13.0

version 0.9.0 for Scala 2.13.0-RC3

use fully qualified references in doc comments

lightbend/genjavadoc#134

Merge branch 'master' into 2.13.x

version 0.9.0 for Scala 2.13.0-M5 only