Compose key for OS X

The compose key is a common way of entering special characters in Linux. For OS X, there are two ways of getting a compose key:

1. With a dedicated keyboard layout such as the ones provided by this project. This has the advantage that it works in all applications and that there is visual feedback while entering the compose sequence.

2. By customizing the Cocoa text system, that is, by editing the file Library/KeyBindings/DefaultKeyBinding.dict. This has the advantage that it is easier to modify and that it will work across different keyboard layouts. It will only work on Cocoa apps, though.