Added .gitignore
Added .gitignore

I copied the recommended version from GitHub for Visual Studio (
https://github.com/github/gitignore/blob/master/VisualStudio.gitignore )
and added a couple of directories specific to Authoring Tools Framework.

JSandusky/ATF,blue3k/ATF,mszymczyk/ATF,twainj/ATF,SonyWWS/ATF,twainj/ATF,mindbaffle/ATF,blue3k/ATF,JSandusky/ATF,mszymczyk/ATF,jethac/ATF,SonyWWS/ATF,mszymczyk/ATF,Nuclearfossil/ATF,jethac/ATF,Nuclearfossil/ATF,Nuclearfossil/ATF,SonyWWS/ATF,gelahcem/ATF,JSandusky/ATF,blue3k/ATF,gelahcem/ATF,gelahcem/ATF,mszymczyk/ATF,mindbaffle/ATF,jethac/ATF,dogdirt2000/ATF,dogdirt2000/ATF,dogdirt2000/ATF,gelahcem/ATF,blue3k/ATF,SonyWWS/ATF,twainj/ATF,twainj/ATF,SonyWWS/ATF,mszymczyk/ATF,JSandusky/ATF,twainj/ATF,dogdirt2000/ATF,blue3k/ATF,mindbaffle/ATF,jethac/ATF,JSandusky/ATF,dogdirt2000/ATF,gelahcem/ATF,jethac/ATF