Facilities for async programming and communication.

go blocks are dispatched over an internal thread pool, which
defaults to 8 threads. The size of this pool can be modified using
the Java system property `clojure.core.async.pool-size`.

Set Java system property `clojure.core.async.go-checking` to true
to validate go blocks do not invoke core.async blocking operations.
Property is read once, at namespace load time. Recommended for use
primarily during development. Invalid blocking calls will throw in
go block threads - use Thread.setDefaultUncaughtExceptionHandler()
to catch and handle.

core.async HIGHLY EXPERIMENTAL feature exploration

Caveats:

1. Everything defined in this namespace is experimental, and subject
to change or deletion without warning.

2. Many features provided by this namespace are highly coupled to
implementation details of core.async. Potential features which
operate at higher levels of abstraction are suitable for inclusion
in the examples.

3. Features provided by this namespace MAY be promoted to
clojure.core.async at a later point in time, but there is no
guarantee any of them will.