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/event_loop.rs

@@ -61,13 +61,13 @@ impl<T> EventLoop<T> {
     }
 
     #[inline]
-    pub fn get_available_monitors(&self) -> VecDeque<MonitorHandle> {
-        monitor::get_available_monitors()
+    pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {
+        monitor::available_monitors()
     }
 
     #[inline]
-    pub fn get_primary_monitor(&self) -> MonitorHandle {
-        monitor::get_primary_monitor()
+    pub fn primary_monitor(&self) -> MonitorHandle {
+        monitor::primary_monitor()
     }
 
     pub fn window_target(&self) -> &RootWindowTarget<T> {