Add a plugin to interact with the github status API.

Mutliple <githubstatus> sections are possible:
* jobs: regexp for jobs to match
* inputs: the input which corresponds to the github repo/rev whose
  status we want to report. Can be repeated
* authorization: Verbatim contents of the Authorization header. See
  https://developer.github.com/v3/#authentication.

src/lib/Hydra/Helper/PluginHooks.pm

@@ -15,7 +15,7 @@ sub notifyBuildStarted {
             $plugin->buildStarted($build);
         };
         if ($@) {
-            print STDERR "$plugin->buildStarted: $@\n":
+            print STDERR "$plugin->buildStarted: $@\n";
         }
     }
 }