add trigger as well as make silent run more silent'er

[cwhittl]

Introduces a trigger capability that allows generating repeats for notes from the past four days when working within a calendar note. This feature is not recommended for regular notes, refer to the repeat extension for that use case.
The trigger line is:
triggers: onEditorWillSave => np.Tidy.generateRepeatsFromRecentNotes.

[jgclark]

I still think adding this trigger isn't the best way to solve this particular problem -- instead use a template to call existing command on daily or weekly notes -- but I'm happy to include it. It does have the advantage of running more frequently for most people, though it has the down-side of lots of repetitive work that may slow the app down.

Changes requested:

• document in the README
• why hard-code to 4 days? There's a "How many days to count as recent?" setting which I think you should re-use here. Though I realise its description will need changing a little as this is not a "Remove ... recent ..." command.

[dwertheimer]

@cwhittl Do you want to keep the conversation going here or should we close the PR?