define 'NAN' in fitcurves.cpp
Merge pull request #5 from CharlyZhang/develop

Define 'NAN' in fitcurves.cpp
Show message in clear(). Clear option for some boolean options.
Support command name: name{'param':value}.
Rename a command name as 'circle2p'. Add getSelectedHandle.
Add kMgNoDel, lockSelShape, lockSelHandle and lockRotateHandle.
Check pointer.
Add getViewModelBox().
Add lockSelShape, lockSelHandle and lockRotateHandle.
Add setShapeFlag and getLastSnappedPoint.
Add getSelectedShapeHandle().
v1.0.51