Make 'git help everyday' work

The "Everyday GIT With 20 Commands Or So" is not accessible via the
Git help system.  Move everyday.txt to giteveryday.txt so that "git
help everyday" works, and create a new placeholder file everyday.html
to refer people who follow existing URLs to the updated location.

Mark up giteveryday.txt so that it formats well with AsciiDoc and
refresh its contents to a more command modern style.

Add 'everyday' to the help --guides list and update git(1) and 5
other links to giteveryday.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Philip Oakley <philipoakley@iee.org>