* Replaces the exit assembly with the function from std.
* Reads the top-of-stack struct at program startup that can get information
  like the pid.
* Changes the read and write functions to use the Pread and Pwrite syscalls
  instead of the depreciated _READ and _WRITE
* Changes the openat function to use flags instead of perms.
  Plan9 does not support perms when opening, just when creating.
* Adds an errstr function to read the errstr buf created by the kernel