Allow verify (prove) multiple identity's (accounts)

It would be easier to prove your (for example) multiple twitter accounts, github accounts and maybe websites (or more) in one Keybase account without creating multiple Keybase accounts that might be confusing to trust you.

The issue proposes proving multiple accounts or websites within one Keybase account, but it names no files, tests, or entry points. Start by identifying the existing identity-verification flow and clarifying the supported account types and trust model; done would mean one account can represent multiple verified identities without requiring separate Keybase accounts.

Written by the indexing model from the issue text.