This moves the kernel to 2^64 - 2^31 (0xFFFF_FFFF_8000_0000) on x86_64, fixing #107 (closed).
While this most likely makes recursive mapping impossible, the need for that on x86_64 is debatable, due to the 128 TiBs of kernel virtual memory, and that the TLB on most systems can contain the entire available physical address space (using 1 GiB pages).
Must be merged together with bootloader!15 (merged).