Publish 2.0.0

[SethTisue]

• wait for scala-collection-compat to publish
• merge PRs
• choose version number
  • 2.0.0
• tag the release and write release notes
  • https://github.com/scala/scala-parser-combinators/releases/tag/v2.0.0
• wait for release build
  • https://travis-ci.com/github/scala/scala-parser-combinators/builds/225891635
• release the staging repos
  • https://oss.sonatype.org/#stagingRepositories
• artifacts on Maven Central
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parser-combinators_3/2.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parser-combinators_3.0.0-RC3/2.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parser-combinators_2.13/2.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parser-combinators_2.12/2.0.0/
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parser-combinators_2.11/2.0.0/
  • (not a complete list)
• any README or build.sbt edits needed?
  • rename 1.2.x branch to 2.x
  • check on 1.2.0-RC2 Native Empty Jar  #380
  • readme updates, post-2.0.0 #388