Publish version 1.0.0-RC1

[SethTisue]

motivations: publish for Scala 3.0.0-RC2, bite the bullet and get to 1.0 (as per #213)

• merge PRs
• choose version number
  • 1.0.0-RC1, as per Release version 1.0? #213
• create the release and write the notes
  • https://github.com/scala/scala-java8-compat/releases/tag/v1.0.0-RC1
• wait for release build
  • https://travis-ci.com/github/scala/scala-java8-compat/builds/221552102
• release the staging repos
  • https://oss.sonatype.org/#stagingRepositories
• artifacts on Maven Central
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_3.0.0-RC2/1.0.0-RC1/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_3.0.0-RC1/1.0.0-RC1/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_2.13/1.0.0-RC1/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_2.12/1.0.0-RC1/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_2.11/1.0.0-RC1/
  • (not a complete list)
• post-release, bump version in README? build.sbt?
  • bump MiMa reference version #218