* implemented breaking a path at a selected point or segment
* implemented joining two subpath at their selected end nodes
* added some helper functions like reversing a subpath, closing a specified subpath or finding a point in the path
* introduced a new type KoPointPosition do describe a path points position inside the path
* added setProperty, unsetProperty functions to the KoPathPoint to add or remove a single point property
* made some documentation updates

There are no commands yet to undo/redo the new functions. I am working on them next.