Add `sys_wait` functions (Fixes #81)

Closes #81

See merge request redox-os/relibc!131

Update `platform::rawfile`

Make functions taking raw pointer return &'a instead of &'static

Simplify cstr_from_bytes_with_nul_unchecked()

The original implementation is modified from the `Cstr` method, but the
complexity there exists because it is trying to convert to the DST `Cstr`.

This is technically more correct, and matches the pointer methods in the
standard library.

Update ralloc. Closes GH-83.

Add optimized version of memchr

Implement clock() and add CLOCK_* constants

stdlib: implement qsort() as an introsort

Fix a bug in printf()

stdlib: implement strtoul() and strtol() using a macro

Because we were previously converting the bytes in the format
string into Rust's char type and then printing that using the
format machinery, byte values that were not valid single-byte
UTF-8 characters failed to print correctly.  I found this while
trying to implement qsort() because the output of my test program
was mysteriously incorrect despite it working when I used glibc.