v4.0.0

• @ledgerhq/web3-subprovider changed signature: createLedgerSubprovider: (getTransport, options) => Provider. the transport is no longer built-in the library, it is externalized on user land. basically you can do createLedgerSubprovider(() => TransportU2F.create()). also note that this will be lazily called at each time (each signature, fetching accounts,..) and close() when work is done.
• TransportU2F was improved. if you use create() you should now have better errors. the breaking change here is that TransportU2F.create() can now fails if the device is not plugged.
  • listen() will error if u2f is not supported.
  • open() will actually check a device presence by sending a mock command to the device. if there is no response, it will timeout with an error.
  • a disconnect event is emit if a "timeout" happens.
• create-dapp starter kit was improved in many ways (see the diff).