A capability-based API modeled after async_std.

This corresponds to async_std.

Capability-based APIs represent access to external resources as values which can be passed around between different parts of a program.

Two notable features are the Dir and Pool types:

• Dir represents an open directory in a filesystem. Instead of opening files by absolute paths or paths relative to the current working directory, files are opened via paths relative to a Dir. The concepts of a process-wide "current working directory" and a single global filesystem namespace are de-emphasized.
• Pool represents a set of network addresses. Instead of allowing applications to request access to any address and then applying process-wide filtering rules, filtering rules are built into pools which may be passed through the program.

On WASI, use of this library closely reflects the underlying system API, so it avoids compatibility layers.

This crate provides a capability-based version of async-std. See the toplevel README.md for more information about capability-based security.