deprecate this package in favor of Intervals.jl

[jrevels]

...as it's strictly more generic. ref https://invenia.github.io/Intervals.jl

Requires a pass to consolidate whatever extra functionality that may be here into there (esp. the notion of a minimal duck-typed interface), then a subsequent pass to update downstream TimeSpans dependents to use Intervals instead.

[haberdashPI]

One note about this: I've been working on some functions to support set operations over TimeSpans (#11). These are much easier to implement if you assume an interval of the form [start, stop), rather than any arbitrary closed/open end points.

[haberdashPI]

If/when this occurs it would be cool to be able to use Unitful values, mostly for the syntax benefits of writing 10s rather than Second(10), but also because I think it is generally easier to work with Unitful values compared Period values.