Bashed random case of header including itself.
Added note to doc/tasks.txt about requiring multithreading.
Rough refactor pass.

- Renamed all variants of subscribe to simply sub.
- scope_guard.* renamed to scope-guard.*.
- Moved event::scoped_sub_c to meta, made into template.
Generalized scoped-sub into scoped-reg.
Shelled task-affinity module.