Win32: basic initialization

Initialization of Win32 with WGL and EGL.

Move variable declarations to beginning of block. Use alloca instead of
dynamically sized arrays. Compiles with MSVC.
Win32 event handling
Win32: special keys and mouse wheel

Handle WM_SYSKEYUP, WM_SYSKEYDOWN, translate keysyms to distinguish
between left and right ctrl, alt, etc.

WM_MOUSEWHEEL, WM_MOUSEHWHEEL send button events.