Add --json flag

[dhleong]

This should suppress all intermediate console logs and just emit a single JSON object (or, when operating on multiple devices such as with search -t, one per line).

[dhleong]

Alternatively, we could have different object "types," and always emit one JSON object per line. So output could look like:

{"type":"log","Searching..."}
{"type":"device","device":{...}}

This would allow ps4-waker to be embedded into apps written in other languages that can call out to the shell, for example. Such a protocol could also be extended to support input from stdin so that the ps4-waker cli app could be used to maintain persistent connections, but that would probably be a separate --rpc flag, or something.