v0.8.0

Refer to the README for this release for detailed instructions.

This is the first public release of the AWS CDK!

• Change license to Apache-2.0 (@RomainMuller in #428)
• Multiple README updates, including animated gif screencast, as preparation for
  public release (@rix0rrr in #433, @eladb in #439)
• Multiple documentation updates for public release (@Doug-AWS in #420,
  @eladb in #436)
• Toolkit (bug fix): Correctly account for CDK::Metadata in cdk diff
  (@RomainMuller in #435)
• AWS CodeBuild (BREAKING): Usability improvements for the CodeBuild
  library (@skinny85 in #412)