Adding a function capable of extracting the name with version out of url/file path

pkgs/lib/strings.nix

@@ -155,4 +155,14 @@ rec {
   # Return true iff string v1 denotes a version older than v2.
   versionOlder = v1: v2: builtins.compareVersions v2 v1 == 1;
 
+  # Extract name with version from URL. Ask for separator which is 
+  # supposed to start extension
+  nameFromURL = url: sep: let
+    components = splitString "/" url;
+    filename = lib.last components;
+    name = builtins.head (splitString sep filename);
+  in
+  assert ! eqStrings name filename;
+  name;
+
 }