Onda is not currently compatible with TimeSpans 0.3

[ericphanson]

Ref #120; I spent some time trying to update the tests there and couldn't figure out the right way to do it. There is some discussion there but I think an issue is probably a good place to discuss in more detail.

The issue comes down to the change from beacon-biosignals/TimeSpans.jl#29 to fix beacon-biosignals/TimeSpans.jl#28 changed the results of indexing an Onda object with a timespan by 1 sample. I argue that the change was a bugfix and the previous behavior was incorrect (see TimeSpans#28 and for even more background, beacon-biosignals/TimeSpans.jl#26). However, this change breaks a bunch of Onda's tests as shown in #120.

I'm not really sure what to do. I wrote https://github.com/beacon-biosignals/AlignedSpans.jl to help the user have more control over the rounding semantics, which provides an alternative to TimeSpans.jl, but that is mostly orthogonal to the issue at hand which probably could be seen as either "TimeSpans made an annoying breaking change to be pedantic and now stuff doesn't work" or "Onda's tests worryingly rely on incorrect behavior from a core dependency" depending on your mood.