add CoinbaseTransfer.from_coinbase_dict
use CoinbaseAmount as the parameter for amounts

This changes the arguments of the CoinbaseAccount methods:

* request
* send
* create_button
remove unused import sure
use non-integer test cb_amount

To make the test just slightly less trivial.
remove allow_transfers=True from test

This now defaults to True, so it isn't necessary.
adjust formatting for line length in tests
adjust formatting
Add (unused) CoinbaseOrder and orders.json