Pixel sizes for fonts

maybe you want to add this. should be dpi independent.

with point size
![point](https://f.cloud.github.com/assets/335438/64661/7a220cce-5e55-11e2-9b09-8bad46c1db25.jpg)

with pixel size (factor 1.4; currently implemented)
![pixel-1 4](https://f.cloud.github.com/assets/335438/64660/7a117cf6-5e55-11e2-81fe-57b431c01dc1.jpg)

with pixel size (factor 1.3; as reference)
![pixel-1 3](https://f.cloud.github.com/assets/335438/64659/7a0d55e0-5e55-11e2-888a-45c73b066940.jpg)