Adds a "do what I mean" multiple-cursor selection with the logic that
I find most useful:
* If there is no active region, mark the next line (or lines, based on
prefix argument)
* If there is an active region that spans multiple lines, call
`mc/edit-lines`
* If there is an active region on a single line, trigger a custom
selection hydra with functionality equivalent to
`mc/mark-more-like-this-extended` but a slightly improved user
experience
Hopefully this will make it easier to get into the habit of actually
using multiple-cursors without calling the mc commands via M-x