added new classmethod PGPSignature.from_sigpkt to reduce code reuse and allow them to be instantiated/installed in list comprehensions
added new classmethod PGPSignature.from_sigpkt to reduce code reuse and allow them to be instantiated/installed in list comprehensions

J08nY/PGPy,J08nY/PGPy,SecurityInnovation/PGPy,SecurityInnovation/PGPy,SecurityInnovation/PGPy