Update to support v0.4

[jrevels]

Hello again! I've been busy with other stuff lately, and haven't been putting time into QuBase.jl.

I believe that QuBase.jl should start targeting the upcoming v0.4 release of Julia. Here are a few reasons:

• It seems that QuBase.jl won't be ready for release until after v0.4 releases anyway (which is planned to be in a couple of weeks, AFAIK).
• Switching over to v0.4 would fix Problem with QuArray type promotion #41
• We'd be able to use Traits.jl, which I think is the right way to standardize interfaces for QuStates and QuOperators so that we can dispatch on behavior without being restricted to specific storage implementations (see my comment in #32).