docs: rewrite index page (including dangling links to future docs) This has been reviewed to death on the evolve-testers mailing list. I've made some minor tweaks since the last round of reviews, but the main content is the same.

amend: add -D/--current-date option, just like mq's qrefresh has Carefully designed so we can easily add -D to other changeset-creating commands (probably anything that takes -d), and so that we can add -U/--current-user as well. When that's done, the date and user options should be very similar to those in MQ.