* In python, Simulation and Particle objects are now picklable. Just like loading Simulations from a binary file, function pointers will need to be re-set manually after unpickling.
* The difference between simulations can now be printed out in a human readable form. Python syntax: `sim.diff(sim2)`. C syntax: `reb_simulation_diff(sim2, sim1, 1)`.
* Reading Simulationarchives with version < 2 is no longer supported.
* The POSIX function fmemopen() is now required to compile REBOUND. This should not affect many users. However, if you are using macOS, the version needs to be >= 10.13 (this version of macOS, High Sierra, was released in 2017).
* Internal changes on how Simulationarchives are written.
* Internal variable names that represent the size of allocated buffers now consistently include the name `N_allocated`.
* The TES (Terrestrial Exoplanet Integrator) has been removed. If you wish to use TES, you will need checkout an earlier version.