Eclipse Californium (Cf) CoAP Framework 2.3.0

The 2.3.0 release comes with changes and bugfixes.

Changes in DTLS:

• supports hello_extension for signature and hash algorithms.
  
  The default changes from "ecdsa_sha256" to "ecdsa_sha256,rsa_sha256".
  
  It's also possible to configure a different list of supported signature and hash
  
  algorithms
• supports x25519 curve for ECDHE (running java 11)
  
  The default curves changes from "secp256r1,secp384r1,secp521r1" to
  
  "secp256r1,x25519,x448,secp384r1". It's also possible to configure a
  
  different list of supported curves.
• Asynchronous PSK store API, supports returning master secret or secret key
• CipherSuiteSelector for more control on selecting cipher suite and parameters
  
  on the server side.

Changes in CoAP:

• add (experimental) peer's based deduplicator to limit maximum number of messages
  
  kept for deduplication.
• improve multicast support and add broadcast support.
• add picocli command-line-interfaces to plugtest clients and servers.

Changes in OSCORE:

• more ciphers supported.
• ID context used to disambiguate retrieving contexts.

Additionally, some bugs have been fixed, please refer to the reflog.