Keeping pid (and file descriptor, and scheme id, ...) as usize is a
footgun. Let's remove it.

* Fire up multiple processors

* Use IPIs to wake up secondary processors

* Much better exception information

* Modifications to show more information on fault

* WIP: Use real libstd

* Add TLS (not complete)

* Add random function, export getpid, cleanup

* Do not spin APs until new context

* Update rust

* Update rust

* Use rd/wrfsbase

* Implement TLS

* Implement compiler builtins and update rust

* Update rust

* Back to Redox libstd

* Update rust

Implement brk

To avoid various bugs regarding the typing of file descriptors, we
newtype them into a simple wrapper type.

- Document some stuff.