Added use of Docker to develop and build packages.

#25 #26 #27

is_connected added
#23

Added support for CEX.io exchange.
Added several parser tests.
#21

Coinbase Pro added

Fixed, method handler can be a coroutine

L2 Bitfinex Book Maintenance Added

Deribit Book Maintenance Added

get_currencies and get_instruments were added to Deribit