add sync command

[chrismerck]

$ python -m bond sync -h
usage: bond sync [-h] [--verbose] [--full] [--print]

options:
  -h, --help  show this help message and exit
  --verbose   Print out all the details of the sync
  --full      Re-sync everything, not just the delta
  --print     Print out the shadow after syncing

Supports incremental update using hash tree:

$ python -m bond sync --verbose
GET ...
GET devices...
GET devices/1...
GET devices/1/skeds...  new:ddf10dc2175096f3  del:f71ba149d50f6ec0
GET devices/1/skeds/ddf10dc2175096f3...

[chrismerck]

Currently doesn't have any use within bond-cli, but I see some things we could build here.

I've added the ability to do bond sync --all --full which would throw away shadows for offline Bonds, useful when switching to another home network. Just --all will do hash-based update for all Bonds in parallel.