Fix class vs typedef of graphics_handle.

Tested with Octave 3.8.0

Signed-off-by: Thorsten Liebig <Thorsten.Liebig@gmx.de>
Minor typo in README fixed

Signed-off-by: Thorsten Liebig <Thorsten.Liebig@gmx.de>
Merge pull request #5 from thliebig/master

Minor fix and typo