Fix memcpy, memmove, memset, and memcmp.

Closes #99

See merge request redox-os/kernel!208

Add QEMU tip.

See merge request redox-os/kernel!206

Context switch optimization

See merge request redox-os/kernel!205

- Contexts for other CPUs will never be evaluated for switch
- Running contexts will never be evaluated for switch
- Arc::clone is only called for previous and next context when there is a context to switch to
- Lots of cleanup to the switch function

Improve text organization.

See merge request redox-os/kernel!202

Kernel notes (moved from CONTRIBUTING).

See merge request redox-os/kernel!201

Pin kmain contexts

Closes #111

See merge request redox-os/kernel!200

Support scheduler CPU affinity.

See merge request redox-os/kernel!199