feat: read-only IPMI driver; report a missing Redfish license (0.2.0)

A Supermicro X10DRL-i refuses Redfish without a license (SUM, DCMS or
OOB), even the service root. IPMI answers without one.

- New entry point `ipmi` (napalm_redfish.ipmi.IpmiDriver) on
  ManagementControllerDriver, over pyghmi: facts and inventory from the
  FRU (serial number, system UUID), the BMC's LAN interface, sensors
  (temperatures, fans, power supplies), the power state, the event log
  and the BMC firmware. Read-only: no power control, no BMC reset.
  Tested against recordings of the X10 with serials, the UUID, MACs and
  IPs replaced.
- RedfishDriver.open() no longer fails on a license refusal: get_facts
  returns what is known without Redfish, get_device_warnings reports
  bmc_license_required with the licenses the BMC names, every other
  getter raises. netOrk then shows the reason instead of an offline BMC.
- IpmiDriver is not exported from the package: NAPALM's own
  get_network_driver("redfish") takes the first driver class of
  napalm_redfish.

napalm_redfish/__init__.py

@@ -1,6 +1,11 @@
-"""NAPALM driver for server BMCs over DMTF Redfish."""
+"""NAPALM drivers for server BMCs: DMTF Redfish, and read-only IPMI as the fallback.
+
+Only ``RedfishDriver`` is exported here: NAPALM's own ``get_network_driver("redfish")``
+takes the first driver class of this package. ``IpmiDriver`` lives in
+``napalm_redfish.ipmi`` and is registered as the ``ipmi`` entry point.
+"""
 
 from napalm_redfish.driver import RedfishDriver
 
-__version__ = "0.1.2"
+__version__ = "0.2.0"
 __all__ = ["RedfishDriver"]