Add missing iostream header
Add example usage of Boost Units library

Create directory to hold examples/tests of using the Boost Units
library. Import performance.cppp example from the current Boost
documentation, adding CMake scripting to build it.
Remove extraneous whitespace
Improve compatibility across Boost versions

Build on platform with older Boost identified an issue with the use
of the "value_name" memebr function of the typed_value class in
program_options. This is only present on Boost 1.50 and higher.

Wrap call to "value_name" in a preprocessor if using Boost's
version macro to only compile it on sufficient Boost.