Fixes https://github.com/prometheus/docs/issues/203

Fix spelling of required.

Fix typo, JXM -> JVM

Move hystrix down to other section, point to SC

Revert #166 and add explanation why the formula is in fact correct.

We're going to drop the hystrix repo from the prometheus
repositry as it's a stale fork. Rather refer
to the original, and put it in the appropriate section.

Link the Clojure client library (wrapper).

Add Heka exporter to list of third-party exporters.

Add blackbox exporter

Add documentation for Marathon SD

Update Kubernetes SD docs

Fixes #202

Document bool modifier

Add Changelog podcast episode to media section.

Remove obsolete reference to closed issue

Minor fixups in etcd discovery blog post.

Add `go get` to the build instructions for the example client.

Kubernetes SD config docs

Fixes #163

Add PostgreSQL exporter to exporter list.

Cross-platform gems for guard watches

Add BIND exporter to list of exporters.

Remove Service Discovery from roadmap.

Document the `__tmp` label prefix.