Add download page

I uploaded the first set of downloads via scp. It seems I can't change the ownership of the files, is that an issue @ibuclaw? I also moved the mingw files I hope there were no public links to the old location, but I don't think the new location on gdcproject.org was ever announced?

The page is auto-generated by using this mustache-file:
https://gist.github.com/jpf91/9464455

The windows builds are unfortunately almost unusable (gdc links to -```lrt```, ```-lpthread``` which are not available, phobos doesn't build), but it can be used with a custom object.d file and -nostdlib so it's not completely useless.
The great thing is that these builds are all done automatically on a x86_64 qemu vm, even the windows->windows ones (these are built as cross-native compilers, a special case of canadian cross compilers).

@ibuclaw if you merge this it might be a good idea to announce this on D.announce to get some attention ;-)

Binaries for the ARM beta will follow later this week.

@venix1 do you have any updated mingw downloads you want published on gdcproject.org?