merge upstream, add tests, full method context

- added benchmarks, and assertions for timeliness
- replaced regex usage in package-name handling with a straight
  comparison to a cached value
- log the fullly-qualified method name, to remove ambiguity
    eg: github.com/fflintstone/yabba.dabba.doo
- clean up possibly-unsafe assumptions about using the standard logger,
  remove global lookup function to enforce safe usage

json_formatter.go

@@ -46,7 +46,7 @@ func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
 		switch v := v.(type) {
 		case error:
 			// Otherwise errors are ignored by `encoding/json`
-			// https://github.com/Sirupsen/logrus/issues/137
+			// https://github.com/sirupsen/logrus/issues/137
 			data[k] = v.Error()
 		default:
 			data[k] = v