Have encoder and writer in place

src/Tools/psxcdgen_ex/src/encoder/psx.rs

@@ -0,0 +1,5 @@
+use super::{SectorWriter, {CDDesc, Error}};
+
+pub fn encode_psx_image(_: CDDesc, _: &mut dyn SectorWriter) -> Result<(), Error> {
+    Err(Error::not_implemented("encode_psx_image"))
+}