Added:

• constants for update operation hints: delete, disable and enable
• type Hint (uint8)
• extended SignHash method with parameter for hint:
  SignHashExtended(name string, hash []byte, protocol ProtocolVersion, hint Hint)

Changed:

• renamed function CheckChain to CheckChainLink
• CheckChainLink now expects structured UPPs instead of bytes as arguments
• adapted tests for new CheckChainLinkfunction signature
• minor refactoring and cleanup

Added:

• validity check for ECDSA private and public keys in key setter methods
• tests for invalid ECDSA key values

Added:

• public function CheckChain(previousUPP []byte, subsequentUPP []byte) which verifies the chain between a previous UPP and a subsequent UPP by comparing the signature of the previous UPP with the "prevSignature" field of the subsequent chained UPP

Removed:

• validity check of UPP in verify method -> only verify signature

Changed:

1. Protocol Implementation:

• verify-method can be used without specifying protocol version of UPP (signed or chained)
  method signature changed from
  func (p *Protocol) Verify(name string, value []byte, protocol ProtocolType) (bool, error)
  to
  func (p *Protocol) Verify(name string, upp []byte) (bool, error)
• decoding functions for signed and chained UPPs now return pointer to object instead of copy of object
• deprecated "plain" message support
• renamed type "ProtocolType" -> "ProtocolVersion" (alignment with naming in UPP documentation/definition: https://developer.ubirch.com/utp.html)
• added more sanity checks

2. Tests:

• added more tests for UPP interface decoding function 'Decode()'
• added tests for signed and chained UPP decoding functions 'DecodeSigned()' and 'DecodeChained()'
• test UPP interface methods after decoding