Show the slowest example groups along with the slowest examples in a report when using `--profile COUNT` (default 10).
Cosmetic changes.
Add example group's filename and line number in the output.
Use the same style as for the examples.
Treat the same doc string in different files as different example groups.
Merge pull request #887 from lfu/master

Show the slowest described classes along with the slowest examples in a report when using `--profile COUNT`