Refine function names and type signatures (#886)

* First name consistency pass. More to come!

* Remove multitouch variable (hopefully this compiles!)

* Remove CreationError::NotSupported

* Add new error handling types

* Remove `get_` prefix from getters.

This is as per the Rust naming conventions recommended in
https://rust-lang-nursery.github.io/api-guidelines/naming.html#getter-names-follow-rust-convention-c-getter

* Make changes to Window position and size function signatures

* Remove CreationError in favor of OsError

* Begin updating iOS backend

* Change MonitorHandle::outer_position to just position

* Fix build on Windows and Linux

* Add Display and Error implementations to Error types

* Attempt to fix iOS build.

I can't actually check that this works since I can't cross-compile to
iOS on a Windows machine (thanks apple :/) but this should be one of
several commits to get it working.

* Attempt to fix iOS errors, and muck up Travis to make debugging easier

* More iOS fixins

* Add Debug and Display impls to OsError

* Fix Display impl

* Fix unused code warnings and travis

* Rename set_ime_spot to set_ime_position

* Add CHANGELOG entry

* Rename set_cursor to set_cursor_icon and MouseCursor to CursorIcon

* Organize Window functions into multiple, categorized impls

* Improve clarity of function ordering and docs in EventLoop

src/platform_impl/macos/mod.rs

@@ -13,10 +13,11 @@ mod view;
 mod window;
 mod window_delegate;
 
-use std::{ops::Deref, sync::Arc};
+use std::{fmt, ops::Deref, sync::Arc};
 
 use {
-    event::DeviceId as RootDeviceId, window::{CreationError, WindowAttributes},
+    event::DeviceId as RootDeviceId, window::WindowAttributes,
+    error::OsError as RootOsError,
 };
 pub use self::{
     event_loop::{EventLoop, EventLoopWindowTarget, Proxy as EventLoopProxy},
@@ -44,6 +45,12 @@ pub struct Window {
     _delegate: util::IdRef,
 }
 
+#[derive(Debug)]
+pub enum OsError {
+    CGError(core_graphics::base::CGError),
+    CreationError(&'static str)
+}
+
 unsafe impl Send for Window {}
 unsafe impl Sync for Window {}
 
@@ -60,8 +67,17 @@ impl Window {
         _window_target: &EventLoopWindowTarget<T>,
         attributes: WindowAttributes,
         pl_attribs: PlatformSpecificWindowBuilderAttributes,
-    ) -> Result<Self, CreationError> {
+    ) -> Result<Self, RootOsError> {
         let (window, _delegate) = UnownedWindow::new(attributes, pl_attribs)?;
         Ok(Window { window, _delegate })
     }
 }
+
+impl fmt::Display for OsError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            OsError::CGError(e) => f.pad(&format!("CGError {}", e)),
+            OsError::CreationError(e) => f.pad(e),
+        }
+    }
+}