Change numpy to np

[davidhassell]

Fixes #278

(No rush on this one!)

[sadielbartholomew]

Brill, thanks. As for closing #278, there are still some import numpy uses in the test suite, based on a git grep "import numpy" and eyeball to see if any lacked the as np at the end at this stage, but it seems you've caught all of the ones outside of it. But maybe we can change those too for this PR, whilst we are at it (though there's an argument to make those all, consistently, import numpy as opposed to the other way round given it is more explicit for testing and we don't seem to use many, if any, as aliases in the test suite at present)?

Either way, happy for you to merge this, though preferably we address the inconsistency in the imports in the test suite too first.

[davidhassell]

Thanks Sadie. Test suite now updated to import numpy as np (82634e3).

[sadielbartholomew]

Thanks @davidhassell for updating this. I've sanity-checked the extra commit and it's all fine, so please merge.