Refactor kernel memory usage

[ddevault]

cc @np511

This currently only contains documentation updates.

[ddevault]

Lots of places in the kernel (and some places in userspace) have to change for each of these changes. I suggest taking it slowly and breaking this up into smaller changes that you can do and test separately.

[ddevault]

All references to threads should be replaced with processes. We'll sort something out for distinguishing threads from processes later, it will be something fairly lightweight.

Also, threadlist should be changed to use http://www.knightos.org/documentation/reference/threading.html#getNextThreadID instead of accessing kernel memory directly.