feat: add pair and unpair support

[erisu]

Resolves #4
Resolves #5

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This PR adds support for pair and unpair.

A successful results would look like this:

{
  status: 0,
  signal: null,
  output: [ null, <Buffer >, <Buffer > ],
  pid: 111,
  stdout: <Buffer >,
  stderr: <Buffer >
}

When pairing is successfully and the stdout was converted to a string, we would see the pair UUID.

Note: The string will contain a trailing newline \n.

[dpogue]

I wonder if it's worth adding { encoding: 'utf8' } as an option to spawnSync everywhere so we get strings back instead of Buffers... it's caused confusion before when it looks like you'll get a string but get a buffer instead

[erisu]

I wonder if it's worth adding { encoding: 'utf8' } as an option to spawnSync everywhere so we get strings back instead of Buffers... it's caused confusion before when it looks like you'll get a string but get a buffer instead

I think adding { encoding: 'utf8' } would be helpful so people don’t unexpectedly get Buffers.

After this PR, I’ll open a separate one that adds { encoding: 'utf8' } to all methods at once, so it will be easy to revert if needed.