Promote PromCon 2017 CfP

Add note about choosing port numbers for exporters on internal
applications. This reflects that the port range is a mere suggestion.

Discussion on prometheus-users is in
https://groups.google.com/d/topic/prometheus-users/S1ZzJMkR1tk/discussion

While the document refers to JMX for Kafka monitoring, unfortunately JMX doesn't expose consumer group stats.

I was told that it was OK to directly sending a PR for this. Please, let me know if it is not.

* added sensu exporter

* sorted

Note extrapolation done in the rate, delta, and increase

As suggested in prometheus/prometheus#2683.

The fork is working, the original one does not even compile any more.

* Added VictorOps configuration to docs

Has been deleted and re-uploaded again by the owner.

Update configuration.md

Signed-Off-By: Joe Handzik <joseph.t.handzik@hpe.com>

Render tarball sha256 checksum if available for release

This is for the 1.6 release of the Prometheus server.

Document that target_label can do regex replacement

Document scrape_samples_post_metric_relabeling and scrape_samples_scraped

Mention timestamped samples cannot yet be scraped

This is just swapping two paragraphs and moves the explanation of the
example after the example itself.

Update storage documentation for the Prometheus 1.6 release

Fixes #602

Fixes #614
Fixes #679