Fix variable-shadowing warning that's new in VC14
OnResize() takes uints for width and height, not ints (what was I thinking?)
Add missing member constructor
Use a uint2 for pixel dimensions of window and render targets, instead of separate width and height members
Support MSAA render targets
Add utility functions for binding the back buffers; also make the depth buffer optional
D3D11Window::Init no longer returns bool - it was pointless, as it never returned false; errors are dealt with by asserts.
Merge master into vc14