for crcanvas 0.16

I. Major Differences from other GTK based canvases
CrItem — The base class for all canvas items and groups.
CrCanvas — A GtkWidget used to paint a tree of CrItem objects.
CrText — A text canvas item that uses PangoLayout.
CrLine — A polygon or polyline canvas item.
CrPixbuf — A item for rendering GdkPixbuf, png files, or a cairo image surface.
CrRectangle — A simple rectangle canvas item.
CrEllipse — A simple ellipse canvas item.
CrVector — A simple two point line vector where the end point can be optionally drawn to device coordinates.
CrPath — A canvas item capable of rendering a cairo_path_t.
CrArrow — An arrowhead that can be used to cap a line segment.
CrInverse — An item group that reverses a transformation higher up in the item tree.
CrBlit — A grouping item to improve performance by caching complex item trees off-screen.
CrRotator — A object for setting up mouse rotation on a CrCanvas widget.
CrPanner — A object for setting up panning on a CrCanvas widget.
CrZoomer — A object for setting up box zooming on a CrCanvas widget.
cr-typesGobject Boxed wrappers for passing data in signals and language wrapping.