Custom type definitions

[dlakaplan]

In __init__.py defining:

# Something that is a Quantity or can behave like one (with units assumed)
quantity_like = Union[float, np.ndarray, u.Quantity]
# Something that is a Time or can behave like one
time_like = Union[float, np.ndarray, u.Quantity, time.Time]
file_like = Union[str, Path, IO]

that can be used elsewhere (instead of exhaustively repeating those).

[dlakaplan]

#1709

[dlakaplan]

Are there other types to add? Or is this sufficient to get started? And should those type definitions by in the top-level __init__.py or elsewhere?

[abhisrkckl]

I think these are good enough to start with. We can add more as needed.

[dlakaplan]

OK, probably ready to merge then. This will simplify a few other in-process PRs.