Add CRG to directly instrumented software

Add Google Stackdriver & Shield exporters to the list of exporters

Document our security model

Include some aspects that may be non-obvious
to a casual user.

Fixes #715

blog: Announce alpha3 and new rule format.

Signed-off-by: Goutham Veeramachaneni <cs14btech11014@iith.ac.in>

See https://github.com/prometheus/alertmanager/blob/master/config/notifiers.go#L238

1.7 Release

Added OpenStack service discovery docs.

This reverts commit b66ec14a.

The PromCon 2017 CfP is closed now.

Directly instrumented applications use a Prometheus client library that
follows our guidelines, and can be used as examples of software doing
that.

Recategorise things accordingly, updating links as needed and
adding some more I know of.
I'm taking Quobyte's word for it that they're directly instrumented,
as it's commercial software and thus I can't check.
kubernetes-mesos has no instrumentation that I can find.

Make absolute links relative in docs

Kumina a company based in the Netherlands doing managed operations for
Linux-based systems. Kumina has switched over to Prometheus over the
last year and is now using it as its exclusive monitoring system for
some of its customers.

In the process, Kumina has developed (and is still developing) metrics
exporters for many pieces of commonly used Open Source software. Most of
these can be found on our company's GitHub page:

	https://github.com/kumina

Kumina is promoting the use of Prometheus and affiliated projects, like
Kubernetes, by giving talks about them at Open Source conferences in the
Netherlands.

Fix typo

Promote PromCon 2017 CfP