[evoggy]

swarm lh write and swarm lh check now take a YAML file with -i/--input, as lh config write -i and lh config check -i do for one Crazyflie:

cfcli swarm lh write -i my_setup.yaml
cfcli swarm lh check -i my_setup.yaml

-i and --config can't be combined; with neither, the configuration the swarm names is used, as before.

Details:

• The configuration is now loaded before the Crazyradios are opened (lighthouse::wanted(), then lighthouse::run()), so a missing or bad file fails at once with its own error.
• When swarm lh check finds Crazyflies that differ, the swarm lh write it suggests now includes the --config or -i that was given. Before, it always suggested plain swarm lh write, which writes the configuration the swarm names.
• docs/swarm.md mentions -i.

Testing

On the fishtank swarm (CF-05 to CF-09, one Crazyradio, base stations 4-7 on):

• Read CF-05's configuration with lh config read -o. swarm lh check -i on that file found all 5 up to date, and swarm lh write -i skipped all 5 as up to date.
• With a copy where BS 4 was moved 3 cm, check -i reported "BS 4 moved 3.0 cm" for all 5 and exited with 60, and its hint named the -i file. write -i --cf CF-05 wrote it, and a check afterwards found CF-05 up to date and CF-06 still differing.
• swarm lh write --cf CF-05 put the swarm's configuration back, and all 5 were up to date again.
• Without a Crazyradio: a missing file and a file that isn't YAML fail with their own error, and --config with -i is refused.
• Unit tests pass.

Closes #42