Successful output is too verbose. Need a -q option

When I run doc8 and there are no violations, I see this:

```
$ doc8 doc CHANGES.rst README.rst
Scanning...
Validating...
========
Total files scanned = 23
Total files ignored = 0
Total accumulated errors = 0
Detailed error counts:
    - doc8.checks.CheckCarriageReturn = 0
    - doc8.checks.CheckIndentationNoTab = 0
    - doc8.checks.CheckMaxLineLength = 0
    - doc8.checks.CheckNewlineEndOfFile = 0
    - doc8.checks.CheckTrailingWhitespace = 0
    - doc8.checks.CheckValidity = 0
```

I don't need to see any of those lines. I'd like a -q option to silence them.