Documentation fixes for Analytics API

This is in response to the [business QA](https://github.com/TrackMaven/TrackMaven/issues/1029) for the analytics API. 

- [x] Updated derived metrics description
- [x] Fixed some broken links
- [x] Added an explanation of the `verbose`  flag with regards to derived metrics
- [x] Fixed an incorrectly explained metrics example
- [x] Added a note about metrics availability being based on third party APIs
"and the [double space] Alexa"