Add logrus, prometheus client and matrix-org/util

vendor/src/gopkg.in/gemnasium/logrus-airbrake-hook.v2/README.md

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+# Airbrake Hook for Logrus <img src="http://i.imgur.com/hTeVwmJ.png" width="40" height="40" alt=":walrus:" class="emoji" title=":walrus:" />&nbsp;[![Build Status](https://travis-ci.org/gemnasium/logrus-airbrake-hook.svg?branch=master)](https://travis-ci.org/gemnasium/logrus-airbrake-hook)&nbsp;[![godoc reference](https://godoc.org/github.com/gemnasium/logrus-airbrake-hook?status.png)](https://godoc.org/gopkg.in/gemnasium/logrus-airbrake-hook.v2)
+
+Use this hook to send your errors to [Airbrake](https://airbrake.io/).
+This hook is using the [official airbrake go package](https://github.com/airbrake/gobrake), and will hit the api V3.
+The hook is synchronous and will send the error for `log.Error`, `log.Fatal` and `log.Panic` levels.
+
+All logrus fields will be sent as context fields on Airbrake.
+
+## Usage
+
+The hook must be configured with:
+
+* A project ID (found in your your Airbrake project settings)
+* An API key ID (found in your your Airbrake project settings)
+* The name of the current environment ("development", "staging", "production", ...)
+
+```go
+import (
+    "log/syslog"
+    "github.com/Sirupsen/logrus"
+    "gopkg.in/gemnasium/logrus-airbrake-hook.v2" // the package is named "aibrake"
+    )
+
+func main() {
+    log := logrus.New()
+    log.AddHook(airbrake.NewHook(123, "xyz", "production"))
+    log.Error("some logging message")
+}
+```
+
+Note that if environment == "development", the hook will not send anything to airbrake.
+
+### Reporting http request failure
+
+
+```go
+import (
+    "log/syslog"
+    "github.com/Sirupsen/logrus"
+    "gopkg.in/gemnasium/logrus-airbrake-hook.v2" // the package is named "aibrake"
+    )
+
+func main() {
+    log := logrus.New()
+    log.AddHook(airbrake.NewHook(123, "xyz", "production"))
+req, err := http.NewRequest("GET", "http://example.com", nil)
+    log.WithField("request", req).Error("some logging message")
+}
+```
+
+Notes:
+
+* the req will be removed from the log entry
+* the name of the field doesn't matter, since it's not logged
+* if more than one request is sent, only the first will be taken into account (and the others will be logged as strings)