Define custom exceptions to support new Pylint v2.16 rule: broad-exception-raised

Since Pylint v2.16, following report is raised:

• W0719: Raising too general exception: Exception (broad-exception-raised)
• Define more precise (sub-set) exceptions:
  • api.ws2p.requests
  • key.signing_key
  • documents

class XxxException(Exception):
    """Raised when xxxx"""

• Bump Pylint to latest version (v2.17+, or v3 if released as stable)
• Silkaj: Remove/fix disable=broad-except in auth.py