Feature Request: Tasks should be filterable on the completed state

A common scenario (if not the most common) when gathering tasks using dataview is likely to be able to pull all tasks that remain incomplete. It would be ideal to be able to do something like the following to filter out tasks that aren’t complete:

task from ""
where !task.complete
sort file.day desc

[blacksmithgu]

I have good news and bad news. The good news is this is now possible; the bad news is you need to write a tiny bit of javascript for it:

```dataviewjs
dv.taskList(dv.pages("#projects").file.tasks.where(t => !t.completed));
```

[blacksmithgu]

This has been on my TODO list forever since it’s conceptually simple, my task query implementation is just a hack. Will improve.