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/test_module.c

@@ -0,0 +1,21 @@
+#include "../test.h"
+#include "../parser.h"
+#include <string.h>
+#include <stdlib.h>
+
+static void test_parser_module_name(void) {
+	Module* m = test_get_ast();
+
+	assert_not_null(m, "expected module to be parsed");
+	assert_str("my_module", m->name, "expected name 'my_module'");
+}
+
+static void test_parser_bad_module_name(void) {
+	test_get_ast();
+	assert_log_file("expected error to be logged for bad module name");
+}
+
+static void test_parser_missing_semicolon_module(void) {
+	test_get_ast();
+	assert_log_file("expected error for missing semicolon");
+}