Change tabs with modifier+digit

I have a very strong muscle memory for changing tabs via `⌘+1`, `⌘+2`,
etc.

Even though it’s a little strange in the FIFO tabs model I got used to
it pretty quickly.
By the way, are you extracting those doc-strings somehow? If not, rehashing what the function does is tedious and error-prone. The chance of me not updating the comment after changing the function is pretty high.