2.9.0

• added new surface tension model (thanks to Fernando Zorilla and Marcel Ritter)
• added a test for reading and writing the state of a simulation
• updated to Eigen 3.3.8
• added a hotkey (m) to rescale the range of the current color map
• color maps range is determined automatically
• all particle fields can now be used for rendering
• improved stability of implicit boundary handling
• improved documentation
• added DebugTools class which generates additional particle data for debugging
• added Python example to add a particle field, this can be used for visual debugging or to export additional data per particle
• updated pybind
• improved warmstart
• added build instructions
• added more colormaps
• improved documentation
• added version file