[CREATE] gbr brush format bumped

[Sven Neumann]

Hi,

perhaps before even talking about the data format, we should try to make
a list of features that we would like to see in a next generation brush
file format. Later we can look at the implementation details.

So let me throw some ideas into the air:

 * grayscale masks
   - more than 8bit should be possible
   - allow different resolutions to improve scaling

 * pixmap brushes
   - should this be image + mask or rather an image with alpha channel?
   - we also need higher bit depths and different resolutions here

 * vector brushes
   - just a set of default shapes?
   - perhaps a subset of SVG? 

 * dynamic brushes
   - based on pixmap and/or vector brushes?
   - more or less complex instructions on how speed, tilt, pressure, ...
     should affect the brush


Sven