Initial delivery of metrics code (#81)

* Initial delivery of metrics code

* Fix build issues

* Fix build issue with go vet

vendor/github.com/prometheus/client_model/ruby/README.md

@@ -0,0 +1,31 @@
+# Prometheus Ruby client model
+
+Data model artifacts for the [Prometheus Ruby client][1].
+
+## Installation
+
+    gem install prometheus-client-model
+
+## Usage
+
+Build the artifacts from the protobuf specification:
+
+    make build
+
+While this Gem's main purpose is to define the Prometheus data types for the
+[client][1], it's possible to use it without the client to decode a stream of
+delimited protobuf messages:
+
+```ruby
+require 'open-uri'
+require 'prometheus/client/model'
+
+CONTENT_TYPE = 'application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited'
+
+stream = open('http://localhost:9090/metrics', 'Accept' => CONTENT_TYPE).read
+while family = Prometheus::Client::MetricFamily.read_delimited(stream)
+  puts family
+end
+```
+
+[1]: https://github.com/prometheus/client_ruby