Add sbrk() and execve() to syscalls
Holy shit huge update

Fixed a shitton of potential problems when it comes to global paging...
hopefully. They haven't actually been problematic yet, so I don't really
know if I've done anything. Don't fix what isn't broke can bite me.
Then, fixed more problems with syscalls (registers being clobbered
mercilessly), messed with execve() so that it copies from userspace
before trashing the old userspace, etc. Long story short, ELF files are
officially executable. You need an OS-specific toolchain, but that's
always the case. As of now, works like a dream for the purposes for
which I have been aiming. It prints to the screen. Woo!