Mention in files that they are made by T. Fukushima and ported

src/accurate/dw0c.rs

@@ -1,3 +1,5 @@
+//! The original implementation of the principal branch of the Lambert W function by Toshio Fukushima, accurate to 50 bits, ported to Rust.
+
 use crate::LambertW0Error;
 
 /// 50-bit accuracy computation of principal branch of Lambert W function, W_0(z),

src/accurate/dwm1c.rs

@@ -1,3 +1,5 @@
+//! The original implementation of the secondary branch of the Lambert W function by Toshio Fukushima, accurate to 50 bits, ported to Rust.
+
 use super::super::{X0, Z0};
 use crate::{LambertWm1Error, LambertWm1ErrorReason};
 

src/fast/sw0.rs

@@ -1,3 +1,5 @@
+//! The original implementation of the principal branch of the Lambert W function by Toshio Fukushima, accurate to 24 bits, ported to Rust.
+
 use super::super::Z0;
 use crate::LambertW0Error;
 

src/fast/swm1.rs

@@ -1,3 +1,5 @@
+//! The original implementation of the secondary branch of the Lambert W function by Toshio Fukushima, accurate to 24 bits, ported to Rust.
+
 use super::super::{X0, Z0};
 use crate::{LambertWm1Error, LambertWm1ErrorReason};