Spray: Build REST/HTTP-based integration layers on top of Scala & Akka

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From the Spray Website:

Spray is a suite of lightweight Scala libraries providing client- and
server-side REST/HTTP support on top Akka.

Fully asynchronous, non-blocking
All APIs are fully asynchronous, blocking code is avoided wherever at all

Actor- and Future-based
spray fully embraces the programming model of the platform it is built upon.
Akka Actors and Futures are key constructs of its APIs.

Especially sprays low-level components are carefully crafted for excellent
performance in high-load environments.

All dependencies are very carefully managed, sprays codebase itself is kept
as lean as possible.

Being structured into a set of integrated but loosely coupled components your
application only needs to depend onto the parts that are actually used.

All spray components are structured in a way that allows for easy and
convenient testing.