add warning log level

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/log/log.go

@@ -8,6 +8,18 @@ func Errorf(format string, args ...interface{}) {
 	Log.Errorf(format, args...)
 }
 
+func Error(args ...interface{}) {
+	Log.Error(args...)
+}
+
+func Warnf(format string, args ...interface{}) {
+	Log.Warnf(format, args...)
+}
+
+func Warn(args ...interface{}) {
+	Log.Warn(args...)
+}
+
 func Infof(format string, args ...interface{}) {
 	Log.Infof(format, args...)
 }