Rename AST structures to Tree and relocate freeing logic

v0/ast/expression.h

@@ -4,37 +4,37 @@
 #include "../bool.h"
 
 typedef enum {
-    EXPRESSION_INTEGER,
-    EXPRESSION_STRING,
-    EXPRESSION_BOOLEAN
-} ExpressionTag;
+    EXPRESSION_TREE_INTEGER,
+    EXPRESSION_TREE_STRING,
+    EXPRESSION_TREE_BOOLEAN
+} ExpressionTreeTag;
 
 typedef struct {
-    ExpressionTag tag;
+    ExpressionTreeTag tag;
     union {
         int integer;
         const char* string;
         bool boolean;
     };
-} Expression;
+} ExpressionTree;
 
 typedef enum {
-    TYPE_EXPRESSION_BUILTIN,
-    TYPE_EXPRESSION_ARRAY
-} TypeExpressionTag;
+    TYPE_TREE_BUILTIN,
+    TYPE_TREE_ARRAY
+} TypeTreeTag;
 
 /**
  * An expression that evaluates to a type.
  */
-typedef struct TypeExpression TypeExpression;
-struct TypeExpression {
+typedef struct TypeTree TypeTree;
+struct TypeTree {
     /** @brief defines which entry in the union is valid */
-    TypeExpressionTag tag;
+    TypeTreeTag tag;
     union {
         /** @brief Evaluates to an array of the given type. */
         struct {
             /** @brief A pointer to the type of the elements stored in the array. */
-            TypeExpression* array;
+            TypeTree* array;
         } array;
         /** @brief Evaluates to a builtin integer type.*/
         struct {