Tracker Announce Subcommand Follow-up

[casey]

There are some things I think would be nice to have for imld torrent announce, but I think they belong in follow-up diffs, to keep the initial diff size. I'm putting them in the same issue so I can keep track of them, but they could easily be broken out into separate issues.

• The warning for non-UDP tracker URLs should be formatted warning: … with warning in yellow.
• It should be possible to pass just an infohash and tracker URL(s) to the CLI (and not a torrent)
• There should be a flag to produce JSON output:

[
  {
    "URL": URL,
    "PEERS": [
      {"IP": IP, "PORT": PORT},
      …
    ]
  },
  …
]