Separate sign and verify from swarm.js

[Flet]

This PR moves the sign and verify logic out of swarm.js and into lib/signature.js.

There are a couple reasons for this:

1. The current sign/verify logic is dependent on the filesystem and will not work in a browser. This separation will allow for an alternative way to sign/verify messages in-browser.
2. There is a need to push swarm.js into its own module so its reusable by peerbot/friends-irc/other bots. Abstracting signature will help to keep this future module focused. Also bots probably don't need to sign/verify.

Please yell at me if this is outrageous. 😁

[Flet]

Hows it work?

Two new functions were added to swarm.js:

swarm.verify(fn)

fn should be a function that takes the arguments username, signature, callback that can be called to verify if the signature belongs to username. the callback is called with err, valid, with valid indicating a true if the signature could be verified.

swarm.sign(fn)

fn should be a function that takes the arguments data, callback and produces a signature for the current user with the specified data. the callback is called with the args err, signature.

signature.js is just a wrapper around ghsign which produces the required functions.

[Flet]

Hmm, can someone check if the @ngoldman merge bot crashed and reboot it? 😎

[ungoldman]

@Flet what these be for?

[Flet]

These are to pass in functions to sign and verify messages.

swarm.js is running these because the signed/verified data is actualy the protobuf-encoded message itself, which is not readily accessible outside the module.

More info in my comment: #129 (comment)

I do agree that the variable name emitter is a little confusing. If it were named swarm it would be a bit more intuitive I think.

[Flet]

also thank you for taking the time to review! ❤️

[ungoldman]

Ah yes I see from #129 (comment). Might be good just to add a comment or two for now so it's clearer for future contributors since at face value they are identical and their purpose is not entirely obvious.

[Flet]

Indeed! The ultimate goal is to move swarm into a nice, well docmented module :). I'll add some code comments so this information is not lost with time.

[Flet]

Comments for the comment god!

[ungoldman]

MERGES FOR THE MERGE KING