Windows CI using AppVeyor
enable 64 bit Julia too
don't fetch --unshallow if repo is complete

This check is necessary if there are fewer commits in the history
than the depth of the AppVeyor clone (currently 50).

Also switch to using regular julia executable, instead of debug version.
The non-debug executable seems to give more useful error messages on Windows.
update Julia nightly download location
Merge pull request #63 from tkelman/appveyor

Windows CI using AppVeyor