Now SpinLock is actually just a spin lock and I added a Mutex that
does the same as the old "SpinLock". This is in preparation for
starting to support smp and making the kernel smp safe. This commit
also removes obsolete PageTableScope and CriticalScope which should
now be used by alternative APIs.
Add "fast page" to KERNEL_OFFSET. This is always present in page
tables and only requires changing the page table entry to map. This
requires no interrupts since it should only be for very operations
like memcpy.
I used to map all temporary mappings to vaddr 0, but this is much
better. C++ standard always says that nullptr access is undefined
and this gets rid of it.
Fixed some bugs I found along the way