Show progress with --progress

```
$ foodcritic . --progress
Food Critic
Checking 15 files
xx.x...........
FC001: Use strings in preference to symbols to access node attributes: ./attributes/default.rb:37
FC019: Access node attributes in a consistent manner: ./attributes/default.rb:37
FC028: Incorrect #platform? usage: ./recipes/default.rb:27
```

I wanted this because I run foodcritic in addition to other tools in sequence, and it's weird to see progress output from others but not foodcritic.

There are also feature specs at https://github.com/justincampbell/foodcritic/compare/progress-output-features, but I couldn't seem to get them working.