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
MMU is can now be locked with RecursiveSpinLock.
Scheduler now has get_current_tid() that works before the Scheduler
is initialized. This allows RecursiveSpinLock usage early on.
MMU moved to namespace kernel
Kernel::Memory::Heap moved to just Kernel
MMU::map_{page,range} renamed to identity_map_{page,range}
Add MMU::get_page_flags
We don't store the error message anymore in BAN::Error.
Instead we store a error code that can be mapped into a string.
This allows BAN::Error to only take 4 bytes instead of 128.
We should also make some kernel initialization just panic instead
of returning errors since they are required for succesfull boot
anyway.