This commit is based on Matt Flax's commits, just slightly polished and
split into logical blocks.

I did not review the code itself, since Stephane has already accepted
Matt's sequence into the codebase, thus indicating he's fine with the
changes.

This reverts commit f08a3f4234.

Renamed JackIIODriver.C -> JackIIODriver.cpp
Renamed JackIIODriver.H -> JackIIODriver.h
Added delete iio_driver when failure is encountered when executing driver_initialize.

Downgraded eigen3 and sox version requirements for building iio.
Switched to using IIOMMap to access the IIO subsystem.
Added the overloaded methods for JackIIODriver::Attach, JackIIODriver::Detach, JackIIODriver::Read and JackIIODriver::Write.
Rewrite the JackIIODriver.C code to work properly.