Add idealised (cartesian) sample for testing purposes

[MaxEtherington]

Added ideal.nc, an idealised cartesian test file, sourced from my current cyclone research.

Included variables are:

• XLAT, XLONG, DZS, U, V, W, REFL_10CM

[lpilz]

Hey Max, thanks for the pull request. Could you also include the Times variable and check if you need other variables by calling .xwrf.postprocess()? We should actually fall back to the XTIME coordinate and I'll work on that in xwrf#169. But in order to get your enhancement merged asap, I'd suggest just adding the Times variable to the data.

[lpilz]

Looks good to me :)

[lpilz]

Actually, I just saw that the west_east_stag dimensions are of size 480 and the west_east dimension is of size 80. Could you make a new pull request (pull your local git first) and either have the west_east_stag size be 81 or just not clip any of the horizontal coordinates? I think either solution would be fine. Thanks :) and sorry I didn't catch that earlier