lots o' updates

aresp - improved error checking
aresp_obj - improved error checking
fencegui - added focusing function for layers (similar to pickgui and
mergegui), added hotkey for intersection switching
mergegui - changed name of “match” to “merge” to better suit behavior,
added polynomial order switching
pickgui - added polynomial order switching, semi-automatic picking of
layers in amplitude space, improved flattening using picked layers
(very similar to mergegui now), removed picking marker