GPIO, IIO, and Shelly device improvments

The MQTT post covered the 0.25 release. Several things have landed since then, mostly around reading real hardware.

• Read a switch or drive a relay from a GPIO line. A gpio node reads or drives one line on a Linux GPIO character device, so a rule can watch a float switch and run a pump. Set the chip to sim to develop rules before the hardware exists. See the GPIO client.
• Analog IO through the Linux IIO subsystem. An iio node reads ADCs, DACs, and the sensors the kernel presents the same way: accelerometers, pressure, humidity, light. Name the device and its channels are detected and added as children, each publishing a reading in volts, amps, or degrees Celsius. See the IIO documentation.
• Shelly devices are more discoverable and efficient. A Shelly Gen2 or later device answers with its own component list, so any such device works, including models released after this one. Status now arrives over a WebSocket instead of polling, so a relay switched at the wall shows up right away. See the Shelly documentation.
• Mirroring a hardware node now creates a view of it, so only the instance where the node actually lives talks to the device, and a value set on the mirror travels back down to the hardware. See primary and mirror edges.
• User passwords are stored hashed. The store, sync streams, and exports carry only a bcrypt hash. Existing passwords convert the next time each user signs in.

Upgrading

Node replies over NATS now use the binary point encoding instead of protobuf. This is an incompatible wire change, so instances and devices that sync with each other need to be upgraded together. The changelog has the full list of changes.