I have finished implementing the memory manager!
free() will now call pmm_free() to free unused pages. At the moment it does not make any difference, but if I want to extend the PMM it will have saved me the work.

Also, I split the demo from the main function so that it is more maintainable.

Log messages with the log level DEBUG will now only appear in debug builds. This made the output much more readable, as you can see in the screenshots.