v2.0.0-rc.6

Since v2.0.0-rc5 the following changes have happened

• Key is verified before cipher suite initialisation
• Expose SelfSign helper and the CCM package
• Make HashAlgorithm private
• Listener is now compatible with stlib net.Listener
• Conn is now compatible with stdlib net.Conn
• New top-level functions CipherSuiteName, CipherSuites
  and InsecureCipherSuites added to match upcoming
  additions to crypto/tls in Go 1.14
• Added support for using context.Context for cancellation
  in Dial, Client and Server
• Where possible the API has been changed to mimic that
  of crypto/tls