Update clientlibs.md

https://github.com/siimon/prom-client seems like the more active and more feature complete project

Fix file_sd syntax

add section regarding Cfg Mgmt contributions

Document URL parameter configuration for Prometheus

Add DigitalOcean hosting to Community page.

Grafana supports prom by default now.

Document query API changes

* optional time parameter in /query
* new HTTP status codes

Clarify the format for file SD files.

This example has confused many potential users who
didn't realise it needed to be put in a list.

Improve storage optimization doc

This addition stems from a recent optimization session at SoundCloud.

Remove wrong anchoring statement for regex matchers

fixes a few simple spelling errors

getting_started.md: cd to unpacked dir

Catch up with Go 1.5.

Remove the example.

Add Benjamin Staffins slides to the media section

Add Apache exporter to list of 3rd party exporters

Prom org url for Docker Hub incorrect

https://registry.hub.docker.com/repos/prom/ no longer works

https://hub.docker.com/u/prom/ seems to work as expected.

Rename statsd_bridge to statsd_exporter

Document the instant rate.

Hamming up the "angry" meaning just a tad.

Use stronger wording for the text format order