multiple sort args

[Kenneth Bingham]

The API supports multiple sort query params as primary, secondary, tertiary, etc. sort priorities. A single sort arg can be passed without an order with the existing query arg like nfctl list networks status=PROVISIONED,sort=createdAt. This works because comma-sep k=v pairs are currently parsed into a dict of params that are fed to the API as query params. The syntax precludes adding a direction like sort=name,desc and so I propose a new arg that accepts a list of space-sep sort params like --sort name,desc createdAt,asc.