Change vector.im -> riot.im on Community page

Vector is Riot now, see:

https://techcrunch.com/2016/09/19/riot-wants-to-be-like-slack-but-with-the-flexibility-of-an-underlying-open-source-platform/

Added GitHub Exporter to documentation

Remove examples of time metrics not using seconds

Bring visualization template example up-to-date

Add interview with Digital Ocean

Added Docker Hub exporter to list of third-party exporters

Fix small grammatical issues w/ AlertManager docs

Add Shuttlecloud user interview

Clarify the Apdex calculation.

The Apdex calculation in the histogram documentation does not actually
match the Apdex as it should be calculated, as any error states should
not be classified as satisfactory of tolerable. This can't be achieved
without including the status code in the http latency labels, which it
is not.

Added missing Exporters to exporter-list

Add standard exports into the documentation

Adds exporters that are still missing in the official documentation up to now. Fixes this.

Replace 1.0 news with PromCon video news on landing page.

PromCon 2016 recap blog post

Prometheus v1.1.0 is released!

Document new date/time related functions.

List unofficial Elixir client

instrumenting: add Rust client library link.

Fix usage of anchored regex in federation example.

file_sd_config: Correct refresh_interval to 5m

The actual default is 5 minutes:
https://github.com/prometheus/prometheus/blob/ee9abf4535d2a28feb14473716e9118b4e12741b/config/config.go#L106

This was changed in prometheus/prometheus@139f27bf8.

Add template to redirect people to docs repo for changes