stm32-metapac: add doc(html_no_source).

The source files are unreadable because they're not fmt'd, and
they take up a LOT of space when generating docs for all 1200 chips
because they don't deduplicate.

stm32-metapac/src/lib.rs

@@ -2,6 +2,7 @@
 #![allow(non_snake_case)]
 #![allow(unused)]
 #![allow(non_camel_case_types)]
+#![doc(html_no_source)]
 
 pub mod common;