general update, updated cimport so it parses struct definitions from imported headers, improved the error reporting, added ifdef and ifndef, added proper support for extern variadic functions, added some new sections and pages to the doc tool and added --check to only check the program corectness and run compile time defs without producing a binary

tests/variadic_extern.meta.json

@@ -0,0 +1,4 @@
+{
+  "description": "Test variadic and non-variadic extern declarations with companion C file",
+  "libs": ["libc.so.6"]
+}