Allow multiple datatype definitions in one file

With our new C-like syntax this was logical to add and simple to
implement.

This closes #81.
No longer allow php-tag syntax

It was poor, unnecessary and confusing.

- Php-tags are for php, not our datatype files. We don't want to make
  people think they are php. With our move towards a C-like syntax, it
  actually looks a lot more like PHP making this a much more pressing
  issue.

- If you can't hide these files from the public some other way, your
  problems are bigger than what we should try to fight. Even on (free)
  shared hosting, you can usually either place your files outside the web
  root or use .htaccess (yes, most shared hosts use apache) to blcok
  access (or both).

- The php tags would do a poor job of hiding it. They would require the
  .php extension to work, basically making this horribly invalid php
  scripts. If you are forced to this mthod, you possibly can't turn off
  showing errors either and thus still are exposing far too much to the
  wide world.