…ect names.

All WinRT builds of SDL will now output, "SDL2.dll".  Previously, the Windows
8.x/RT builds would output, "SDL.dll", and Windows Phone 8 builds would output,
"SDL_WinPhone.dll".  The change to "SDL2.dll" puts WinRT dll naming in-line with
that seen on Win32.

SDL/WinRT's MSVC project files will now appear as either "SDL2-WinRT" or
"SDL2-WinPhone", when displaying in MSVC.

This set of changes should not break any older WinRT or Windows Phone 8 app
builds that rely on MSVC's Project-to-Project reference system to build SDL2 for
the correct platform(s), and to install SDL2 dll files into the apps' output
packages.  App builds that reference SDL dll files directly should, however,
now reference "SDL2.dll".