Feature/#36 non standard shifted keys

These are my first additions to allow defining keys for entering chars, that are normally only accessible by pressing AltGr(the right alt) and some key when the os keyboard layout is set to some european layouts.

Additionally I added some macros to enter otherwise dead keys directly. If I want to enter for example ~, I need to press AltGr and + twice.
Should probably be removed (also for the other macros in this pull request) since it isn't true.  It's true for the original macros because they're used in ".../lib/layout/keys.h", and so need to be defined before that file is included.