This turned out way better than the old code. ELF loading is now quite
straightforward, and we don't need the weird concept of subregions anymore.
Next step is to respect the is_writable flag.
We don't do anything useful with the data yet, but I'm gonna rewrite
the layout code to run off of the program header table instead.
This will allow us to map .text and .rodata sections in read-only memory.
This took me a couple hours. :^)
The ELF loading code now allocates a single region for the entire
file and creates virtual memory mappings for the sections as needed.
Very nice!
We load /_hello.o which just prints out a simple message.
It executes inside the kernel itself, so no fancy userspace process
or anything, but this is still so cool!
