Merge branch 'master' into authentication

Conflicts:
	zerorpc/core.py
Modify authentication middleware adapting the latest middleware api change.
Revert "Add custom Event class support in Server and Client."

This reverts commit 10a1fe03e2bce627393dc6f88591f71344a54818.

Conflicts:

	zerorpc/core.py
	zerorpc/events.py
	zerorpc/socket.py