Tidy and document monero-bulletproofs

I still don't like the impl of the original Bulletproofs...

coins/monero/ringct/clsag/src/lib.rs

@@ -5,7 +5,8 @@
 
 use core::ops::Deref;
 use std_shims::{
-  vec, vec::Vec,
+  vec,
+  vec::Vec,
   io::{self, Read, Write},
 };