Add scaladoc for TreePathSelected and short references in Tree and Tree#selection. Rename path arguments in TreePathSelected because they were confusing.
fixes multiple NPE problems with Tree. fixes calls to JTree's getLastSelectedPathComponent, getSelectionPaths, getClosestPathForLocation, getEditingPath. Also rectifies return type of editingPath.
Merge pull request #3 from Sciss/master

TreePathSelected documentation and argument names.

Great stuff Sciss, thanks for your contribution!  Sorry for the delay in merging.