Create runtests.jl

[IainNZ]

This will allow PackageEvaluator to run the tests in this package using an X virtual framebuffer.

I excluded canvas.jl because it doesn't seem to work - I think because using an if isn't well defined.

[nolta]

Thanks, except:

• examples.jl, issues.jl, & plot.jl aren't separate tests, but part of compare.jl.
• compare.jl diffs the current output of Winston against a baseline set of images, which are created the first time the test is run. I'm not sure this will work with PackageEvaluator.

[nolta]

(oops, wrong button)