heuristics regexp engine configurable #2, skip rules at runtime

regex/regex.go

@@ -0,0 +1,9 @@
+package regex
+
+// Package regex abstracts regular expression engine
+// that can be chosen at compile-time by a build tag.
+
+const (
+	RE2       = "RE2"
+	Oniguruma = "Oniguruma"
+)