Rename construct to construct_nfa and improve tests

lib/include/construct.h

@@ -9,6 +9,6 @@
 #include "fsa.h"
 #include "regex.h"
 
-void construct(const regex_t *regex, fsa_t *out);
+void construct_nfa(const regex_t *regex, fsa_t *out);
 
 #endif