Profile performance cost of directives and extractions

**Issue by [jrudolph](https://github.com/jrudolph)**
_Tuesday Feb 10, 2015 at 16:11 GMT_
_Originally opened as https://github.com/akka/akka/issues/16836_

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See also spray/spray#342

Also see [this thread](https://groups.google.com/forum/#!topic/spray-user/CgC7ftxlBmM).

/cc @sirthias

The issue names no files or tests; start by reviewing the linked spray/spray#342 issue and the referenced spray-user discussion. Determine which directive and extraction costs need profiling, and consider the work complete when the requested profiling scope and results are documented.

Written by the indexing model from the issue text.