Fix case_statement/lambda-close-over-variables bug, rename ast_node file to make ast_node:: unambigious, change test_ast to test_compiler and add a little skeleton c_generator file

stdlib/importer.krak

@@ -7,7 +7,7 @@ import util:*
 import string:*
 import mem:*
 import io:*
-import ast_node:*
+import ast_nodes:*
 import ast_transformation:*
 import parser:*