* docs: add references to app.whenReady() in isReady
* refactor: prefer app.whenReady()
In the docs, specs, and lib, replace instances of `app.once('ready')`
(seen occasionally) and `app.on('ready')` (extremely common) with
`app.whenReady()`.
It's better to encourage users to use whenReady():
1. it handles the edge case of registering for 'ready' after it's fired
2. it avoids the minor wart of leaving an active listener alive for
an event that wll never fire again
* docs: add clipboard paste Fiddle example
* docs: add clipboard copy Fiddle example
* docs: add appropriate title to Fiddles
Co-Authored-By: John Kleinschmidt <jkleinsc@github.com>
