Add optional debugging to scripts

If scripts are executed with DEBUGGING environment variable set, they will dump
a more verbose output during execution.
Add a KHEAP_END address constant
Reorder paging includes
Improve output from paging kernel panics

Decode information from CR2 and display.
Revert the memset() and memcpy() functions to uint8_t
Bodge major page fault regression

For reasons unknown to me, the kernel became unbootable. The problem was
caused by the creation of the kernel heap. This would cause a page
fault at address KHEAP_START (0xC0000000). By trial-and-error, I found a
value that works, however this is not a suitable solution, and the
regression should be pursued further.