Make size/position types generic over pixel type (#1277)

* Begin implementing DPI generics

* Fix multithreaded example

* Format

* Fix serde test

* hopefully fix most of the errors

* Fix dpi module errors

* More error fixings

* Format

* fix macos errors

* Another error pass

* Replace bad type signatures

* more fixins

src/platform_impl/web/stdweb/mod.rs

@@ -33,7 +33,7 @@ impl WindowExtStdweb for Window {
     }
 }
 
-pub fn window_size() -> LogicalSize {
+pub fn window_size() -> LogicalSize<f64> {
     let window = window();
     let width = window.inner_width() as f64;
     let height = window.inner_height() as f64;