Bugfix: Correctly free old assignments when reloading

Fixes #516

include/regex.h

@@ -17,6 +17,12 @@
  */
 struct regex *regex_new(const char *pattern);
 
+/**
+ * Frees the given regular expression. It must not be used afterwards!
+ *
+ */
+void regex_free(struct regex *regex);
+
 /**
  * Checks if the given regular expression matches the given input and returns
  * true if it does. In either case, it logs the outcome using LOG(), so it will