Sink creator function

Just started working on a creator function, called to_sink(), which will allow sinks to be generated in situ from free functions. A little like a bind, just not as complicated (I hope).

An example of use would be:

std::copy(files.begin(), files.end()
  , ff::format_iterator(ff::to_sink(::OutputDebugString)

                      , "\t{0}\n"));

Hopefully I should have something releasable in the next week or so.