Use number_with_delimiter when printing stats

This commit improves the view:

![before](https://cloud.githubusercontent.com/assets/10076/5132312/3c32986a-70b0-11e4-88d6-edd72b5ecf78.png)

making it look like:

![after](https://cloud.githubusercontent.com/assets/10076/5132310/3c1df9a0-70b0-11e4-9763-f19b06538534.png)
Merge pull request #752 from claudiob/print-stats-with-delimiter

Use number_with_delimiter when printing stats