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/parser/core.c

@@ -0,0 +1,52 @@
+#include "internal.h"
+#include "../str.h"
+#include "../log.h"
+#include <stdlib.h>
+
+void parser_next_token(Parser* p) {
+    p->token = tokenstream_next(p->ts);
+}
+
+bool parser_accept(Parser* p, TokenType token) {
+    if (p->token.token == token) {
+        parser_next_token(p);
+        return true;
+    }
+    return false;
+}
+
+bool parser_expect(Parser* p, TokenType token, const char* msg) {
+    if (parser_accept(p, token)) {
+        return true;
+    }
+    log_on_line(&p->token.location, msg);
+    return false;
+}
+
+bool parser_peek(Parser* p, TokenType token) {
+    if (p->token.token == token) {
+        return true;
+    }
+    return false;
+}
+
+bool parser_require(Parser* p, TokenType token, const char* msg) {
+    if (parser_peek(p, token)) {
+        return true;
+    }
+    log_on_line(&p->token.location, msg);
+    return false;
+}
+
+char* parser_to_text(Parser* p) {
+    char* str = string_copy(p->token.text);
+    parser_next_token(p);
+    return str;
+}
+
+bool parser_accept_primitive(Parser* p) {
+    return parser_peek(p, TOKEN_I8) || parser_peek(p, TOKEN_I16) || 
+           parser_peek(p, TOKEN_I32) || parser_peek(p, TOKEN_I64) ||
+           parser_peek(p, TOKEN_U8) || parser_peek(p, TOKEN_U16) || 
+           parser_peek(p, TOKEN_U32) || parser_peek(p, TOKEN_U64);
+}