When using Linux you may use Compose KeysCompose Keys and map the right control, for example, to be the Compose key. This can be done under Keyboard/Keymapping settings tool of your Desktop Manager. Then you'll be able to use several default mappings as well as create your own set of key mapping. I was not able to use Compose Keys on OS/X although they work well on FreeBSD.
link for https://en.wikipedia.org/wiki/Compose_key because it is a difficult concept