Only `sampledBy` is past tense

[mAAdhaTTah]

I don't know if this is a huge deal, but I think it's a little odd that, of the "Combine 2 Observables" methods, sampledBy is the only one written in past tense. The others are all filterBy, bufferBy, etc. I'd like to propose deprecating sampledBy in favor of sampleBy, making all of them consistently present tense.

I don't know if / when we're considering a 4.0, but that's probably a long-future away anyway, so deprecating and changing this over might be worth doing now and thinking about what we may want to include in a (potential) 4.0 release.