gnu: Add rust-permutohedron.

* gnu/packages/crates-io.scm (rust-permutohedron): New variable.

gnu/packages/crates-io.scm

@@ -860,6 +860,28 @@ the @code{take_while} predicate returned false after dropping the @code{by_ref}.
     (license (list license:asl2.0
                    license:expat))))
 
+(define-public rust-permutohedron
+  (package
+    (name "rust-permutohedron")
+    (version "0.2.4")
+    (source
+      (origin
+        (method url-fetch)
+        (uri (crate-uri "permutohedron" version))
+        (file-name (string-append name "-" version ".tar.gz"))
+        (sha256
+         (base32
+          "0b1pzh48j86v46wxngch6k1kx9cdw3jr3lwa86gd6jd4bmxzz1xn"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/bluss/permutohedron")
+    (synopsis "Generate permutations of sequences")
+    (description
+     "Generate permutations of sequences.  Either lexicographical order
+permutations, or a minimal swaps permutation sequence implemented using Heap's
+algorithm.")
+    (license (list license:asl2.0
+                   license:expat))))
+
 (define-public rust-pin-utils
   (package
     (name "rust-pin-utils")