Add basic function call parsing.

src/libabacus.c

@@ -69,6 +69,10 @@ libab_result libab_register_function(libab* ab, const char* name, libab_function
         result = LIBAB_MALLOC;
     }
 
+    if(result == LIBAB_SUCCESS) {
+        result = libab_convert_lex_result(eval_config_add(&ab->lexer.config, name, TOKEN_FUN));
+    }
+
     if(result == LIBAB_SUCCESS) {
         result = libab_table_put(&ab->table, name, new_entry);
     }