Add (|!>) operators

These operators (|!>) and (<!|) ideally should be called (!>) and (<!) but the problem is that (!>) is unary and it turns out it will be the most used of the 2, because it's in the direction of typical F# pipes.

Author: gusty

src/FSharpPlus/Operators.fs

@@ -174,6 +174,18 @@ module Operators =
     /// <category index="1">Functor</category>
     let inline iter (action: 'T->unit) (source: '``Functor<'T>``) : unit = Iterate.Invoke action source
 
+    /// <summary>
+    /// Replaces a functor value with the supplied one, ignoring the original value.
+    /// </summary>
+    /// <category index="1">Functor</category>
+    let inline (|!>) (source: '``Functor<'T>``) (value: 'U) : '``Functor<'U>`` = Map.Invoke (fun _ -> value) source
+    
+    /// <summary>
+    /// Replaces a functor value with the supplied one, ignoring the original value.
+    /// </summary>
+    /// <category index="1">Functor</category>
+    let inline (<!|) (value: 'U) (source: '``Functor<'T>``) : '``Functor<'U>`` = Map.Invoke (fun _ -> value) source
+    
     /// <summary>
     /// Un-zips (un-tuple) two functors.
     /// </summary>