Feature: Additional thread safe bus instance wrapper

[felixdivo]

This PR adds a thread safe wrapper around existing interfaces. Calls to send() and recv() are locked independently.

# this
from can import Bus
bus = Bus(bustype='some_interface', channel='0')

# becomes this
from can import ThreadSafeBus
bus = ThreadSafeBus(bustype='some_interface', channel='0')

In that case, the locking of send_periodic() is disabled since it is redundant.

Testing and docs are still left to be done.

[felixdivo]

Okay, it does not work like that. Any help is appreciated.

[felixdivo]

I will wait a while with this until #277 gets finalized & merged.