Summarize the operation in the top level hash key

This pull requests aims to make it easier to read the contents of a mongo instrumentation event.

### Before
![Schermafbeelding 2013-04-11 om 17 25 52](https://f.cloud.github.com/assets/1336311/368284/38a434b0-a2bc-11e2-8105-a531ccb23aad.png)

### After
![Schermafbeelding 2013-04-11 om 12 18 32](https://f.cloud.github.com/assets/1336311/368290/412aa9fc-a2bc-11e2-88dc-caf0f069b85b.png)