Sign the installers

[User]

> It's all about removing resistance and raising the level of 
> professionalism.  D isn't a hobby project and shouldn't act 
> like one. This is an obvious barrier that's worth removing.  In 
> this day and age of rampant actively dangerous software, it's 
> an obvious improvement to sign it and make the strong claim 
> that this is produced and vended by the d foundation and we 
> vouch for it's contents.  We already do for some (all?) of the 
> posix distribution bundles.


Well said, thanks.