Nickname search

It's possible to search for someone on keybase using only their name; even if you don't know a username or keybase handle, the search bar will return these results. A quick example of this that I found while exploring this is user `digitalfx`'s profile, none of whose usernames are related to his name. If you search just his full name, this profile comes up.

That's great, but I think keybase could benefit from a more robust name search. My name is Timothy, and that's what my keybase profile says. But most people call me Tim, and my profile is pretty hard to find using just that nickname. Even though my last name is currently unique on the website, searching "Tim" with my last name doesn't bring up any results (but searching just my last name will find my profile just fine).

Even without adding a nickname dictionary, I don't think it's unreasonable to try searching just for a person's last name if the data in the search bar includes a space; this would solve my own problem, such that a person searching my first and last name but using my nickname would still find me. You'd come up with a lot of false positives, though. I think the best solution is to have a dictionary for common nicknames (Tim, Mike, Joe, etc.) and fall back on last name search on people with more obscure first names.

Start by reviewing the existing Keybase people-search behavior described in the issue. Compare nickname matching with the proposed last-name fallback, and clarify which approach should be implemented. Done means searches using a common nickname plus a last name can find the intended profile without unacceptable false positives.

Written by the indexing model from the issue text.