#28 Register .mod extension to BoardMod

[Michael Prager]

create a registry file to register the "mod" extension
with Windows, and then add a context menu to Windows
itself, so you can right-click on a mod file in Windows
Explorer, and have the option to somehow automatically
install that mod or open it in YaME

Adding BM3 to the Open With/Choose Program would be
nice too

the .mod extension should be added during the
installation instead of manually also added to the new
context menu