Further isolation of _get_data
Fix RGB overlays to scale image using scaling method in model
Rename link to viewer in canvases
Added a Path object that can be added or drawn to the canvas
Added Square and Ellipse to canvas drawing types

NOTE: tk/agg interface does not have Ellipse type
Enhanced graphics types + redrawing bug fix

- added isosceles Triangle (previous triangle becomes RightTriangle)
- added Box type
- added Ellipse type
- added new style to Point (now have "cross" or "plus")
- Boxes, Triangles, Ellipses, and Polygons can take a rot_deg
    parameter to rotate the item about its own center

- fixed a bug where the display would get corrupted after a rotate if
    changing contrast
- bumped release
refactor
Merge branch 'master' of https://github.com/ejeschke/ginga
bugfix