Add optional Serde implementations and missing derivable traits (#652)

* Add optional serde feature

* Document features in README

* Add changelog entry

* Implement some missing derivable traits

* Add changelog entry for std derives

* Remove extraneous space on serde doc comments

* Add period to end of serde line in readme

* Remove serde impls from WindowAttributes

* Add serde impls for TouchPhase

* Add serde test file

* Add feature lines to testing CIs

* Remove WindowAttributes from changelog

src/lib.rs

@@ -92,6 +92,9 @@ extern crate libc;
 extern crate log;
 #[cfg(feature = "icon_loading")]
 extern crate image;
+#[cfg(feature = "serde")]
+#[macro_use]
+extern crate serde;
 
 #[cfg(target_os = "windows")]
 extern crate winapi;
@@ -199,7 +202,8 @@ impl std::fmt::Debug for EventsLoop {
 /// Returned by the user callback given to the `EventsLoop::run_forever` method.
 ///
 /// Indicates whether the `run_forever` method should continue or complete.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum ControlFlow {
     /// Continue looping and waiting for events.
     Continue,
@@ -357,7 +361,8 @@ impl std::error::Error for CreationError {
 }
 
 /// Describes the appearance of the mouse cursor.
-#[derive(Debug, Copy, Clone, PartialEq)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum MouseCursor {
     /// The platform-dependent default cursor.
     Default,