Terminal client for keybase chat

If you are on desktop, your options for using Keybase for interactive chat are either to run the Electron desktop app, or to run a sequence of `keybase chat send` and `keybase chat read` commands. The former isn't great from a security perspective (Electron apps are a notorious security problem due to the bundled browser and libraries), and _personally_ I don't like having more applications open than I need to. So, I have opted to (for now: #22140) use the command-line interface itself, paired with a [little demon](https://github.com/jonhoo/keybase-chat-notifier) that notifies me when I have new messages.

This works, but is _very_ cumbersome. If I get a message, I run `keybase chat read ` (which I think is also not tab-completeable?), get a list of messages, type `keybase chat send `, type my response in something is almost, but not quite, a `readline` environment, and then send. If they reply, I then repeat the process again and again.

It would be very handy if there was a (simple) TUI for having interactive chat sessions. Something straightforward like an ncurses interface for a _single_ conversation would help enormously. All it would need is to show new messages as they arrive, and allow me to type messages to respond. I _think_ this is all buildable through `keybase api`, but before I sit down and try to hammer something together myself, I figured I'd open an issue here in case this is something you've already thought about.

Start by reviewing the existing `keybase chat send` and `keybase chat read` commands and the `keybase api` entry point. Done means a terminal interface for one conversation that displays new messages as they arrive and lets the user type and send replies.

Written by the indexing model from the issue text.