Fix all memory leaks

Debugged via valgrind
The tree freeing was leftover from single-spaced binary tree.

header.c

@@ -55,6 +55,8 @@ static int read_entry(struct BIT_BUFFER *bitbuf, struct tree *parent)
 		free(c);
 	}
 
+	free(bit);
+
 	return 0;
 }
 

huffman.c

@@ -11,18 +11,13 @@
 
 void free_tree(struct tree *parent)
 {
-	while (parent != NULL) {
-		struct tree *left, *right;
+	if (parent == NULL)
+		return;
 
-		left = parent->left;
-		right = parent->right;
+	free_tree(parent->left);
+	free_tree(parent->right);
 
-		if (right != NULL)
-			free(right);
-
-		free(parent);
-		parent = left;
-	}
+	free(parent);
 }
 
 long get_file_size(FILE *file)