Kombu-pyamqp-threadsafe

Feat

- KombuConnection.default_channel now threadsafe
- new method KombuConnection.from_kombu_connection() to recreate thread-safe KombuConnection from already exists kombu.Connection
- add env KOMBU_PYAMQP_THREADSAFE_DEBUG to logging more details about locks; maybe in feature added some other info

Fix

- now KombuConnection correctly check internal transport when replace it via thread-safe variant (previously it's always raise error)
- now KombuConnection.default_channel_pool allow return channel to pool back if it reusable; ensure connection is connected when create pool

Feat

- now KombuConnection by default use "shared" transport version (previously you should use `add_shared_amqp_transport` or `monkeypatch_pyamqp_transport` functions)

Feat

- initial