New Features

zigpy_znp.tools.nvram_reset resets a device.
zigpy_znp.tools.nvram_write takes a -r argument to reset a device after writing new firmware.
zigpy_znp.tools.nvram_write now allows firmware downgrades back to unsupported versions of Z-Stack.
If a TRACE logging level exists (must be equal to 5 or named TRACE, and be more verbose than DEBUG), zigpy-znp will log very verbose messages with that level. Otherwise, DEBUG will be used.

Changes

Increase minimum zigpy version to 0.23.0.
Drop the attr package as a dependency.
Add autodetection for the CC2531 and slae.sh's CC2652R USB stick
Limit concurrent requests to 2 for CC2531 and 16 for more capable coordinators (can be overridden with the max_concurrent_requests setting). Future releases may intelligently limit requests in response to memory errors.
VERBOSE and TRACE logging is available in all command line tools, defaulting to INFO.

Fixed bug where a callback responding to one of multiple ZDO requests of the same type would be erroneously accepted by all.
Networks formed with a channel mask and a fixed channel did not always use the fixed channel. ` is used in the configuration