Publish 1.0.0

[SethTisue]

motivations: publish for Scala 3.0.0

• merge outstanding PRs
• update crossbuild
  • add Scala 3.0.0 to crossbuild (and drop -RC2) #229
• choose version number
  • 1.0.0
• create the release and write the notes
  • https://github.com/scala/scala-java8-compat/releases/tag/v1.0.0
• wait for release build
  • https://travis-ci.com/github/scala/scala-java8-compat/builds/225881822
• 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_3/1.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_3.0.0-RC3/1.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_2.13/1.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_2.12/1.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-java8-compat_2.11/1.0.0/
  • (not a complete list)
• post-release, bump version in README? build.sbt?
  • yes, see discussion on Release version 1.0? #213
  • update readme and build, post 1.0.0 #231