merge ignacio's gtk3 branch
adding support for collaboration -- so far, just circle objects
add collaboration; fix bug with pause button
more news for v15
clean up radio buttons
use icon_value
work-around radio button selection issue
more tweaks to radio buttons
add sharing to polygons and magic pen
v16
reference sl#305 in comment
chain tool draws curves
fix index bug
fix drag problem with touch
find_body doesn't return a list
news for v19
elements cleanup
Merge branch 'master' of github.com:walterbender/physics into gtk3
cleanup
Merge branch 'master' of github.com:walterbender/physics