Simple setImmediate shim

 setImmediate allows scripts to yield to the browser, executing a given
 operation asynchronously, in a manner that is typically more efficient and
 consumes less power than the usual setTimeout(..., 0) pattern. This library
 provides a simple setImmediate shim.
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 This library is a dependency of readdirp. Even though setimmediate is
 packaged, patching readdirp to use it is more work.
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 Node.js is an event-based server-side JavaScript engine.