alternate loop re-run determination

[SEAPUNK]

Using keypresses is sloppy and causes problems.

Sometime in the next version, we will want to add a "callback" function that has the return value (or the error), and a function that you can use as a "remote control": Call with "true" to rerun the loop, and "false" to stop the loop and continue execution.

It will take care of all caveats, except for the internal module state one.

That, and make hotato usable in production (with reservations).

• Add callback option, which will disable logging to console, and using stdin.
• Add to README.
• semver-major Require an explicit mode in the arguments, so we don't have to default to console.log()/keypress.