Add function to free tree nodes.

src/tree.c

@@ -0,0 +1,22 @@
+#include "tree.h"
+#include <stdlib.h>
+
+void libab_tree_free(libab_tree* tree) {
+    int free_string = 0;
+    int free_vector = 0;
+    if(tree->variant == BASE || tree->variant == OP ||
+            tree->variant == UNARY_OP || tree->variant == BLOCK ||
+            tree->variant == FUN || tree->variant == IF ||
+            tree->variant == WHILE || tree->variant == DOWHILE ||
+            tree->variant == FOR || tree->variant == CALL ||
+            tree->variant == RETURN) {
+        free_vector = 1;
+    }
+    if(tree->variant == ID || tree->variant == STR || tree->variant == NUM ||
+            tree->variant == KW || tree->variant == OP || tree->variant == UNARY_OP ||
+            tree->variant == FUN || tree->variant == CALL) {
+        free_string = 1;
+    }
+    if(free_string) free(tree->string_value);
+    if(free_vector) vec_free(&tree->children);
+}