Remove copy-assign and copy-ctor from Output.

So we aren't lying when we say the rhs is const any more.
Explicitly define move ctors for Windows.

We need to define move constructors for types holding Outputs by name
because VS2013 isn't compliant with the C++11 spec.
http://msdn.microsoft.com/en-us/library/hh567368.aspx

Clang does the right thing and generates default move constructors for
us.

In the worst case, we should be able to explicitly declare the move
constructor as `default`, but VS2013 doesn't support this (yet?).
http://msdn.microsoft.com/en-us/library/dn457344.aspx
const-correctness for supplant.

The supplanted Output is non-const, so we move it.
Remove old code.
Merge pull request #16 from sansumbrella/non-copyable-output

Make Output<T> non-copyable