Verify messages signed with Bitcoin address

I had an interesting issue today where I needed to publicly securely caution people about trusting things coming from me on social media, as I was concerned that my accounts had been compromised (2FA saved the day, it seems).

I posted a PGP-signed message on Facebook and Google Plus, then tweeted a shorter message followed by a tweet with a signature generated by my Bitcoin client since PGP signatures are too large for Twitter.

However, I realized after posting an [all-clear message](https://twitter.com/colindean/status/505568142907949056) and [signature](https://twitter.com/colindean/status/505568353831092224) that it's not as easy for people to verify Bitcoin signatures as it is for PGP signature (or, at least as easy as Keybase has made it).

What if Keybase had a feature where a user could create a link to Keybase that contains both the message and the signature, so that people could easily verify it?

Perhaps the URL would look something like this:

```
https://keybase.io/colindean/verify/bitcoin?message=It%20appears%20that%20there%20was%20actually%20no%20breach%20of%20my%20social%20media%20or%20email%20accounts.%202FA%20FTW.%20Trust%20as%20normal.&signature=H0Y7dSGMRPQlUBD9bwrY6%2B26QPB%2BH%2B8YPOcIz7m2zrzKJYYPpfhjJOrZyOVxZE0uM86g4oS9S05zHCSGKrki5qc%3D
```

Without those parameters, a user is prompted to fill in the message and signature, and can get the URL to use in a tweet or post or something.

This could drive traffic to Keybase while providing a useful feature from the cryptocurrency community to the world by enabling the broadcast and quick verification of messages with short signatures.

No files, tests, or entry points are named. Start by clarifying the proposed verification URL and the Bitcoin signature behavior it must support, then locate the Keybase website or client verification entry point. Done means users can create or open a link containing a message and signature and verify it reliably.

Written by the indexing model from the issue text.