Moved the SIO files to a new sio/ folder.
Added the 'version.h'stuff, added Makefile rule to generate the Manifest file for Windows.
Re-worked the About dialog - it now includes more info.
The symbol DIDEVTYPE_JOYSTICK gets defined only if DIRECTINPUT_VERSION
is < 0x700, but then all DX8 symbols are missing. This probably works
just fine with mingw headers.
Since it's only one symbol that's missing, we'll just define that
locally
