Added managed callback example
Re-indent to 4 spaces, add doc comment
Modify managed-callbacks example to make the use case more obvious
Rename example to better fit with the changes
Merge pull request #35 from bjz/managed-callbacks

Added managed state example
Use new formatting macros
Update Drop impl

`&self` was changed to `&mut self` in a recent update to std
Merge branch 'master' of git://github.com/bjz/glfw-rs into q3