implement LArray.from_dict or from_dict top-level function

[gdementen]

def from_dict(d):
    return LArray(list(d.values()), Axis(d.keys()))

[gdementen]

and/or modify behavior of LArray(dict) which currently creates a "scalar" LArray with the dict, which is a bit weird.

[gdementen]

stack(d) could work for this use case, but it currently does not.
It assumes that if we pass a dict, we need a real Axis object (to get labels order). On Python 3.7, this is no longer a necessary precaution. And even on Python < 3.7, this is annoying when you do not care about the order. Maybe changing the assert into a warning for python < 3.7 would be the right move, or even no warning in the code but a warning in the doc? After all when you iterate on a dict it does not output a warning.

[alixdamman]

As long as we add one or several examples, no warnings at all seems fine to me.