Fix typo: my -> may

Merge next-release into master

fixes #221

The 'labels' setting in the global configuration section has been renamed to 'external_labels' and now has changed semantics. Hence, the fix.

Fixes https://github.com/prometheus/docs/issues/180

Improve docs around random example build prerequisites.

Add FLOSS Weekly interview to Media page.

Update wording around "Tabular"/"Console" view.

https://github.com/prometheus/docs/issues/226

Fixes https://github.com/prometheus/docs/issues/225

Document new name and semantics of external labels.

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