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.

lib/initcode.S

@@ -0,0 +1,25 @@
+#include "syscall.h"
+#include "traps.h"
+
+.code64
+.section .text
+.global start
+
+start:
+  lea init(%rip), %rdi
+  lea argv(%rip), %rsi
+  mov $SYS_exec, %rax
+  syscall
+
+exit:
+  mov $SYS_exit, %rax
+  syscall
+  jmp exit
+
+init:
+  .string "/bin/init"
+
+.p2align 3
+argv:
+  .quad init
+  .quad 0