Add touch pressure information for touch events on Windows (#1134)

* Add touch pressure information for touch events on Windows

* Modified CHANGELOG.md and FEATURES.md to reflect changes

* Updated documentation of struct Touch to reflect changes

* Replaced mem::uninitalized() with mem::MaybeUninit
Fixed warnings in platform_impl/windows/dpi.rs

src/platform_impl/windows/dpi.rs

@@ -1,6 +1,6 @@
 #![allow(non_snake_case, unused_unsafe)]
 
-use std::{mem, os::raw::c_void, sync::Once};
+use std::sync::Once;
 
 use winapi::{
     shared::{