Add Equatable conformance to NoError

[natestedman]

To allow use with functions dependent on Equatable conformance, i.e.

let foo = Result<Int, NoError>(value: 10)
let bar = Result<Int, NoError>(value: 10)

foo == bar

[mdiep]

This seems fine to me. Anyone have a reason why we shouldn't?

[NachoSoto]

I can see that there might be philosophical/mathematical reasons why this doesn't make sense, but I think in practice it does.

[ikesyo]

Is this intentionally targeted to swift2.x branch, not master (Swift 3) ?

[mdiep]

I'm embarrassed to say that I didn't notice which branch it was targeting. 😞