Removed mutable fields.
Merge pull request #7 from Kimundi/master

Removed mutable fields.
Remove sigils on extern fns
Update for glfw api changes
Update examples to use glfw::Window::{should_close, set_should_close}
Use newtype structs for Monitor and Window types
Remove unnecessary Window::destroy calls in examples
Use Option methods to simplify callbacks
Changed namespace resolution; prive -> unstable rename
Merge pull request #8 from Kimundi/master

Changed namespace resolution; public impl; privat -> unstable rename
Move callback helper functions to separate module and generate them using macros
Fix import
Add a temporary fix for X11 and Win32 crash
Refactor macros a little to make them easier to understand
Remove usages of to_unsafe_ptr
Remove return value on the window close callback in line with the glfw api changes
Improve naming in preparation for adding messaging
Remove temporary fix for X11 and Win32 crash

This has now been fixed in GLFW: https://github.com/elmindreda/glfw/commit/aec952e8dce2bab1f71a11d4b554d58c816fa20f
Remove deprecated GLFW 2.x key names
Use spawn_sched to make spawning the task on the main thread cleaner