Rebound

* Various minor bug fixes. Added pre-timestep modifications for REBOUNDx.

* Various minor bug fixes. One related to exact_finish_time=1.

* Added real-time interactive 3D visualizations using WebGL for Jupyter notebooks. This is an early release. Not everything might be working yet and new feature will be added to the widget class. To try it out, simply run `sim.widget()` in a Jupyter notebook. Note that you need to have ipywidgets installed and enabled.
* Minor changes to the Visualization backend. This should not have any consequences for users.

* Now stores the first characters of the current githash in binary files. This is helpful when trying to restart simulations from a binary file and making sure one uses the same version of REBOUND than in the original run. Currently, the git hash is not automatically compared when reloading a binary file. To view the githash, use e.g. hexdump. The hash appears between the first and second zero character in the first 64 bytes of the file.

* Updated visualization. REBOUND now uses a modern version of OpenGL (3.3) that allows for custom shaders and therefore better looking visualizations. However, REBOUND now requires glfw3 to compile the visualization module. If you are on a Mac, then the easiest way to install the glfw3 library is with homebrew: `brew tap homebrew/versions && brew install glfw3`. If you are on Linux, you can install it with your package manager, for example with `sudo apt-get install libglfw3-dev`.

* Introducing the Simulationarchive. The Simulationarchive allows for exact (bit-by-bit) reproducibility in N-body simulations and a completely new way of analyzing simulations. See Rein&Tamayo (2017) for details.
* The binary format has changed. Binary files created with an earlier version of REBOUND can not be loaded with this version. However, future binary files will be backwards compatible from this point forward.


Version 2.x