Refactor AST and Parser into modular subdirectories

- Split ast.h into granular headers in v0/ast/
- Split parser.c into modular implementation files in v0/parser/
- Move and rename parser tests to v0/parser/test_*.c
- Update build system (include.mk) with modular sub-makefiles
- Maintain v0/ast.h and v0/parser.h as umbrella headers

v0/ast.h

@@ -4,124 +4,8 @@
 #ifndef AST_H
 #define AST_H
 
-#include "bool.h"
-#include "token.h"
-
-#include <stddef.h>
-
-typedef struct {
-    /** @brief The name of the module being imported. */
-    char* module_name;
-
-    /** @brief Whether the import is public or not. */
-    bool is_public;
-} ImportDeclaration;
-
-typedef enum {
-    EXPRESSION_INTEGER,
-    EXPRESSION_STRING,
-    EXPRESSION_BOOLEAN
-} ExpressionTag;
-
-typedef struct {
-    ExpressionTag tag;
-    union {
-        int integer;
-        const char* string;
-        bool boolean;
-    };
-} Expression;
-
-typedef enum {
-    TYPE_EXPRESSION_BUILTIN,
-    TYPE_EXPRESSION_ARRAY
-} TypeExpressionTag;
-
-/**
- * An expression that evaluates to a type.
- */
-typedef struct TypeExpression TypeExpression;
-struct TypeExpression {
-    /** @brief defines which entry in the union is valid */
-    TypeExpressionTag 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;
-        } array;
-        /** @brief Evaluates to a builtin integer type.*/
-        struct {
-            /**
-             * @brief The number of bits in the integer.
-             * Typical values are 8, 16, 32, and 64.
-             */
-            int bitSize;
-            /** @brief `true` if the type is signed, `false` if it's unsigned. */
-            bool isSigned;
-        } builtin;
-    };
-};
-
-/**
- * A declaration that aliases one type to another.
- */
-typedef struct {
-    /** @brief The name of the alias. */
-    const char* name;
-
-    /** @brief The value of the alias. */
-    TypeExpression value;
-} AliasDeclaration;
-
-/**
- * A declaration of a variable, which may be a constant or not, and may be static or not.
- */
-typedef struct {
-    /** @brief The name of the variable. */
-    char* name;
-
-    /** @brief The type of the variable. */
-    TypeExpression type;
-
-    /** @brief The optional initializer expression. */
-    Expression* initializer;
-
-    /** @brief Whether the variable is public or not. */
-    bool is_public;
-
-    /** @brief Whether the variable is static or not. */
-    bool is_static;
-
-    /** @brief Whether the variable is a constant or not. */
-    bool is_const;
-} VariableDeclaration;
-
-/**
- * The top-level model.
- * Every file matches an entire Module.
- */
-typedef struct {
-    /** @brief The name of the module. */
-    char* name;
-
-    /** @brief The list of imports in the module. */
-    ImportDeclaration* imports;
-
-    /** @brief The number of imports in the module. */
-    size_t import_count;
-
-    /** @brief The list of aliases in the module. */
-    AliasDeclaration* aliases;
-
-    /** @brief The number of aliases in the module. */
-    size_t alias_count;
-
-    /** @brief The list of variables in the module. */
-    VariableDeclaration* variables;
-
-    /** @brief The number of variables in the module. */
-    size_t variable_count;
-} Module;
+#include "ast/expression.h"
+#include "ast/declaration.h"
+#include "ast/module.h"
 
 #endif