Fix extra argument behavior

[canyon289]

Same question as before though! Why force people to use keyword argument?

[ColCarroll]

Cool - looks like this change turned up a few legitimate bugs like the one you pointed out in #188:

************* Module arviz.tests.test_xarray_utils
arviz/tests/test_xarray_utils.py:111:15: E1121: Too many positional arguments for function call (too-many-function-args)
************* Module arviz.plots.densityplot
arviz/plots/densityplot.py:64:20: E1121: Too many positional arguments for function call (too-many-function-args)
************* Module arviz.plots.forestplot
arviz/plots/forestplot.py:161:21: E1121: Too many positional arguments for function call (too-many-function-args)

[ColCarroll]

Oh, and I wanted a positional argument so the library would be more explicit and readable. It is easy to remove in the future, but hard to add back in. If it gets too annoying, we can remove!

[ahartikainen]

It will make usage more robust. Especially important for plotting library where users have used other libs before (e.g mpl)

[ahartikainen]

especially important if we go with multiple backends

[canyon289]

Oh, and I wanted a positional argument so the library would be more explicit and readable. It is easy to remove in the future, but hard to add back in. If it gets too annoying, we can remove!

You mean you wanted a keyword argument?

Makes sense and I agree, by forcing people to use keywords itll make it way easier to make changes without breaking peoples code later.

[ColCarroll]

Oof, sorry, yes, keyword argument.