Add blank lines after module-level //! comments.

Most modules have such a blank line, but some don't. Inserting the blank
line makes it clearer that the `//!` comments are describing the entire
module, rather than the `use` declaration(s) that immediately follows.

crates/core_simd/src/ops/assign.rs

@@ -1,4 +1,5 @@
 //! Assignment operators
+
 use super::*;
 use core::ops::{AddAssign, MulAssign}; // commutative binary op-assignment
 use core::ops::{BitAndAssign, BitOrAssign, BitXorAssign}; // commutative bit binary op-assignment

crates/core_simd/src/ops/deref.rs

@@ -2,6 +2,7 @@
 //! Ideally, Rust would take care of this itself,
 //! and method calls usually handle the LHS implicitly.
 //! But this is not the case with arithmetic ops.
+
 use super::*;
 
 macro_rules! deref_lhs {