Bundling and splitting

It might be nice to be able to declare a single context that includes many "sub-contexts", then split it up into those parts as needed.

Examples:

• Full I/O capabilities of a "regular process"
  • Output only
  • Networking
  • Clocks
• Async executor
  • Task spawner
  • Timer management

Syntax

If we use the more argument-like syntax to define context types, we could reclaim = for this:

#![allow(unused)]
fn main() {
context foo;
context bar;
context baz;

context kaboodle = foo + bar + baz;
}