"now" won't return current Unix time if perf presented

I've tried using `Signal.Time.every` in a Elm-like fashion (sending messages with a Unix timestamp applied), but instead it returns time from the session (kinda) start, because it relies on `performance` and `process`, using `Date.now` as a fallback only.

The closest workaround is copying `everyP` and re-implementing `now` in own foreign module.

But either or both:
* the documentation really should note that moment (from which JS object it takes current time)
* `every` instance for Unix time dispatching should be presented

Start by tracing Signal.Time.every, everyP, and now, especially how they use performance, process, and Date.now. Decide whether the intended fix is to document which JavaScript time source is used or to provide an every variant that dispatches Unix time, then verify the chosen behavior against the issue's workaround.

Written by the indexing model from the issue text.