v0.4.0

Changed

• Breaking changes:
  • decode now borrows the XQR instead of taking ownership of it
    • This allows the XQR to be reused after decoding
  • encode takes an issuer rather than key id
  • fetch_public_key takes an issuer in addition to key id
    • This allows the issuer to be used to fetch the public key and look up by key id
• Change from jwt-simple to jwtk