Make it possible to easily generate time series

This is a follow-on idea from #8540, particularly https://github.com/astropy/astropy/pull/8540#issuecomment-482948959 and https://github.com/astropy/astropy/pull/8540#issuecomment-484507538 . The idea is to add another way of creating TimeSeries by doing time.series() (where time is a Time object).

TBD: whether keywords should be allowed to have more control of TimeSeries creation - e.g. adding more data columns.

(I’m initially milestoning it for 4.0 but it could get pulled up to 3.2 as a quick follow-on to #8540 if I find time and someone can review it by tomorrow.)

[astrofrog]

I’m not fully convinced we really need this - after all, the Zen of Python says

There should be one-- and preferably only one --obvious way to do it.

What would be the benefit of being able to do Time.series? Would it be for use in contexts other than the TimeSeries class?

Would it make more sense to focus on making sure that e.g. np.linspace works for Time as @mhvk mentioned in #8540?

[astrofrog]

I can try and clarify the docs next week! Indeed you can just do TimeSeries(time=timeobj, data=...)