added trim merge mode

This quadratic function will shift the center of the first axis using
the second one, while keeping the whole range of motion.
Added GUI changes for merge == 3

Trim merge mode option and text added to the GUI
syntax correction

removed incorrect semicolons from pasted code. The trim mode works fine
now.
Merge pull request #4 from PhoenixBvo/master

PhoenixBvo's trim merge mode addition