Use underscore instead of period for generated topic names

[JacobCrofts]

It looks like we only have two Pub/Sub topics in production right now, configured here and here. The topic names in these config files all follow the format topics/${apiName}_v#{versionNumber}-${resourceName}, even though the autogenerated ones from Reslang assume that there will be a period between the apiName and versionNumber instead of an underscore.

I propose that we change the "standard" such that we use an underscore instead of a period, because:

• that's what everybody is doing already (in what is a marvelous coincidence... I'm guessing Taxonomy copy/pasted from Segment or the other way around)
• if we don't, then Taxonomy and Segment will either have to change their topic names in order to make their docs correct (which is more work), or manually edit their docs after every events spec generation so that they are correct (which is more work and carries risk)

[ops-github-DU4JOAWE]

This change is 

[JacobCrofts]

cc @LiveRamp/dev-taxo since your team has the same problem: we're calling our Pub/Sub topics one thing, but Reslang is calling them another, so the events docs we publish have the wrong topic name.

[njaczko]

Ah, would you mind also adding a one-line description to https://github.com/LiveRamp/reslang/blob/master/docs/releases.md ?

You can use this if you'd like: Revert generated topic name format for compatibility with topic names generated by earlier versions of Reslang.