Eliminate specific version numbers from examples and docs to extent possible

[lance]

In general, the version specific comments throughout these docs will have a short shelf life.

https://github.com/cloudevents/sdk-javascript/pull/141/files#r424509323

This is generally true. We should, as much as possible, find a way to eliminate these from the docs and examples except where it can't be avoided - e.g. providing a version number to an emitter to ensure that an event is transported via a specific spec version.

[lholmquist]

@lance i can take a look at this if it is still open?

[lance]

It's all yours @lholmquist :)

[grant]

Won't this version of the README/code be invalid when the spec reaches 2.0 and a user clones the old version?