Created Failable<Bool, T>.toggle() method

Sources/Validation/Failable+Helpers/Failable+Bool.swift

@@ -0,0 +1,7 @@
+extension Failable where T == Bool {
+    
+    /// See [`Bool.toggle()`](https://developer.apple.com/documentation/swift/bool/2994863-toggle).
+    public mutating func toggle()throws {
+        try self <~ !self.value
+    }
+}