Alright, so my general idea of creating/killing threads is as follows:

When a new thread is spawned, it happens through fork, so the new thread gets a
new thread ID but keeps the process ID of the parent process. The new thread is
added to a doubly linked list of thread IDs with the same common process ID.
When a thread is promoted to a process, the process ID becomes that thread ID
(helps with finding threads and corresponding process IDs). Should check that no
other process is using that ID, but it should be exeedingly rare if not
impossible. (can't think of how you would launch 4B threads on one machine but I
guess that's not impossible?)

All threads share a common (struct vm_branch), and only when a thread is
elevated to a process is a new one allocated. Only when the last thread in a
process is released is the memory released. Will still need to figure out
exactly how device memory should be freed, since it's handled globally instead
of per thread atm.

Also, I suspect I may have made my life a bit too difficult with different sized
pages, as I'm having a hell of a time figuring out how `fork` should be
implemented :D
