Substitutions are now done after differentiating / integrating (fixes #145)

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Zoom level is now preserved when rotating the screen (fixes #144)

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
add legal notes
Merge remote-tracking branch 'arian/master' into work