Feature request: support for Meetup profiles

Many of us use [Meetup](https://www.meetup.com/) to join cool events and meet cool new people. In professional circles LinkedIn is used to connect pretty often, but I can see Keybase really fitting this niche where people want to quickly verify the identity of people they've just talked to at a meetup. If Meetup was supported by Keybase, no one has to share calling cards, wonder if they're connecting with the right person in LinkedIn or sending an email to a spam address. Well, you guys know why you created Keybase in the first place... Meetup would be a great addition.

The issue names no files, tests, or entry points. Start by reviewing how existing external profile integrations are represented and determine which Keybase components would need Meetup support; done should include a defined integration scope and verified Meetup profile behavior.

Written by the indexing model from the issue text.