Allow configuration of different log formats: text, json

Signed-off-by: Vlad Ungureanu <vladu@palantir.com>

log/context.go

@@ -37,9 +37,17 @@ type (
 	loggerKey struct{}
 )
 
-// RFC3339NanoFixed is time.RFC3339Nano with nanoseconds padded using zeros to
-// ensure the formatted time is always the same number of characters.
-const RFC3339NanoFixed = "2006-01-02T15:04:05.000000000Z07:00"
+const (
+	// RFC3339NanoFixed is time.RFC3339Nano with nanoseconds padded using zeros to
+	// ensure the formatted time is always the same number of characters.
+	RFC3339NanoFixed = "2006-01-02T15:04:05.000000000Z07:00"
+
+	// TextFormat represents the text logging format
+	TextFormat = "text"
+
+	// JSONFormat represents the JSON logging format
+	JSONFormat = "json"
+)
 
 // WithLogger returns a new context with the provided logger. Use in
 // combination with logger.WithField(s) for great effect.