Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

include/sleeplock.h

@@ -0,0 +1,9 @@
+// Long-term locks for processes
+struct sleeplock {
+  uint locked;       // Is the lock held?
+  struct spinlock lk; // spinlock protecting this sleep lock
+
+  // For debugging:
+  char *name;        // Name of lock.
+  int pid;           // Process holding lock
+};