* [init] support compiling initcode

* [init] use execve instead of exec in initcode

[syscall] migrate to linux-like syscall

#8 resolved
#9 resolved

* [mm] lazy alloc

* [mm] uvmfree for lazy

* [mm] uvmcopy for lazy alloc

* [mm] uvmalloc for lazy

* [mm] lazy alloc and CoW

userspace program now brokes

Syscall added:
getppid
getgid
getuid
setgid
setuid