Added create_user.php, which allows us to directly add a user record to
the database using POST data from an HTML form sent with AJAX/javascript.
At this point we've pretty much done all the dirty work to make our
project work. We can get any information we want, and we can post any
information we want in the form of a JSON object.

Now, we can design our frontend in earnest. The most complicated part of
this will be the calendar, which we should begin looking into immediately.