Check for AltGr if replacement equals to input

If replacement equals to input, no replacement is made, because
there's apparently nothing to do. However, there may be something
to do if AltGr was pressed. For example, if a layout is built in
a way that allows typing the original character instead of
the replacement by pressing it with AltGr. This happens in
a layout for the Udmurt language.
Add doc about altGr in the code
Merge pull request #151 from amire80/altGr_not_noop

Check for AltGr if replacement equals to input