Add ability to change the min/max size of windows at runtime (#405)

* Add min/max size setting for win32 and wayland backends

* Implement dynamic min/max size on macos

* Add min/max size setting for x11

* Add empty functions for remaining platforms

* Improved min/max size setting for x11

* Added CHANGELOG entry for new min/max methods

* Added documentation for new min/max methods

* On win32, bound window size to min/max dimensions on window creation

* On win32, force re-check of window size when changing min/max dimensions

* Fix freeze when setting min and max size

src/platform/linux/x11/util.rs

@@ -1,11 +1,54 @@
 use std::mem;
 use std::ptr;
 use std::sync::Arc;
+use std::ops::{Deref, DerefMut};
 use std::os::raw::{c_char, c_double, c_int, c_long, c_short, c_uchar, c_uint, c_ulong};
 
 use super::{ffi, XConnection, XError};
 use events::ModifiersState;
 
+pub struct XSmartPointer<'a, T> {
+    xconn: &'a Arc<XConnection>,
+    pub ptr: *mut T,
+}
+
+impl<'a, T> XSmartPointer<'a, T> {
+    // You're responsible for only passing things to this that should be XFree'd.
+    // Returns None if ptr is null.
+    pub fn new(xconn: &'a Arc<XConnection>, ptr: *mut T) -> Option<Self> {
+        if !ptr.is_null() {
+            Some(XSmartPointer {
+                xconn,
+                ptr,
+            })
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, T> Deref for XSmartPointer<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.ptr }
+    }
+}
+
+impl<'a, T> DerefMut for XSmartPointer<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.ptr }
+    }
+}
+
+impl<'a, T> Drop for XSmartPointer<'a, T> {
+    fn drop(&mut self) {
+        unsafe {
+            (self.xconn.xlib.XFree)(self.ptr as *mut _);
+        }
+    }
+}
+
 pub unsafe fn get_atom(xconn: &Arc<XConnection>, name: &[u8]) -> Result<ffi::Atom, XError> {
     let atom_name: *const c_char = name.as_ptr() as _;
     let atom = (xconn.xlib.XInternAtom)(xconn.display, atom_name, ffi::False);