Add method to set re class for any rspamd regexp

src/libutil/regexp.c

 	regexp_id_t id;
 	ref_entry_t ref;
 	gpointer ud;
+	gpointer re_class;
 	guint64 cache_id;
 	gint flags;
 	gint ncaptures;
 
 	return re->id;
 }
+
+gpointer
+rspamd_regexp_get_class (rspamd_regexp_t *re)
+{
+	g_assert (re != NULL);
+
+	return re->re_class;
+}
+
+gpointer
+rspamd_regexp_set_class (rspamd_regexp_t *re, gpointer re_class)
+{
+	gpointer old_class;
+
+	g_assert (re != NULL);
+
+	old_class = re->re_class;
+	re->re_class = re_class;
+
+	return old_class;
+}

src/libutil/regexp.h

  */
 guint64 rspamd_regexp_set_cache_id (rspamd_regexp_t *re, guint64 id);
 
+/**
+ * Get regexp class for the re object
+ */
+gpointer rspamd_regexp_get_class (rspamd_regexp_t *re);
+
+/**
+ * Set regexp class for the re object
+ * @return old re class value
+ */
+gpointer rspamd_regexp_set_class (rspamd_regexp_t *re, gpointer re_class);
+
 /**
  * Create new regexp cache
  * @return