Fixed typo in a Mouse.getPosition overload name, fixes #53.

Signed-off-by: Patrick Dinklage <pdinklag@googlemail.com>
Update Rect classes to handle negative dimensions correctly according to the actual SFML code. Fixes #51

Signed-off-by: Patrick Dinklage <pdinklag@googlemail.com>
Updated SFML to 2.1.

Signed-off-by: Patrick Dinklage <pdinklag@googlemail.com>