Winrt fix

This gets the vc2012_winrt project building again, after the winrt stuff fell behind from various updates.  Tested with a handful of the samples in the `samples/_directx` folder and everything seems to be working okay.

@andrewfb For the unicode stuff I just changed where they were calling the old `ci::toUtf16/8()` methods to the ones you put in CinderMsw.h, which is really wchar / `std::stringw`. I'm not sure if you want this stuff to be using proper utf16 strings, but in any event it is how it was when MSOpenTech handed this code off.

One other thing to note, I didn't update the [winrt-specific boost headers](https://github.com/cinder/Cinder/tree/dev/include/winrt/boost), since everything seems to work fine, I thought best not to open that bag..

Fixes #465