Export isstrided

[lkdvos]

Closes #30

[Jutho]

Is this not exported in StridedViews?

[lkdvos]

It is, but it does not get pushed through.
I guess the question is more something along the lines of:
Should an end-user, that requires Strided.jl, also import StridedViews.jl?
Right now, all exports from StridedViews (except for isstrided) are just re-exported, and it is quite convenient to not have to import both. Additionally, I do feel like isstrided could be part of the public interface.