Put unit exports behind a submodule?

[ssfrr]

It seems a little rude perhaps to export 1-letter names like s to the users namespace without asking (particularly if they're running mostly unitless), so I'm wondering whether it's better to force an explicit using SampledSignals.Units if you want to use the short unit exports.

I figure that there are going to be some breaking changes coming up, so now would be a good time to make this change.

@haberdashPI do you think that's reasonable or just adds inconvenience for users?

[haberdashPI]

I somehow missed this. That seems completely reasonable to me! I've wondered that myself.