SVG representations of geometry objects

Produces a SVG representation of the geometry object (with 0,0 in the lower left hand corner) that is used by _repr_svg_ in BaseGeometry to render the geometry in iPython notebook.

Signed-off-by: Henry Walshaw <henry.walshaw@gmail.com>
Colour representations on valid invalid

Change implementation to give visual feedback on geometry.is_valid - if valid the geometry will be blue, invalid will be red.

Signed-off-by: Henry Walshaw <henry.walshaw@gmail.com>
Merge pull request #121 from om-henners/ipython_notebook_svg

Ipython notebook svg