Rebound

* Added new 'reb_simulation_add_fmt()' function. This makes adding particles in C as easy as in python.
* Orbits can now also be initialized using the eccentric anomaly.
* Fixed an issue which prevented one loop in the gravity routine form being parallelized with OpenMP.
* Added a warning message when test particles have finite mass.
* More reliable reading of corrupt Simulationarchive files.

* MERCURIUS: If encounters only involve test-particles (type 0), then the algorithm is now resetting the coordinates of all massive particles after the encounter step. This only changes the outcome at the machine precision, but it makes the trajectories of massive particles independent of the close encounter history. Thanks to Kat Deck for this feature!
* MERCURIUS: The gravity routine is now $O(0.5 \cdot N^2)$ instead of $O(N^2)$ for non-OPENMP runs. This should lead to a noticable improvement in runtime.

* Orbital parameters of particles can now be changed in-place. For example: 'sim.particles[1].e += 0.1'.
* Implemented more chatty repr functions for most object. Printing REBOUND objects should now give some useful information.
* Improved support for adding/removing particle in MERCURIUS during collisions.
* REBOUND now outputs an error message when one is trying to remove a particle with a negative index.
* Small updates to the documentation.
* New ipython example added, showing how to use a python collision resolve function.

* Due to a bug, WHFast was not thread-safe. It is now.
* Random number generator seed is now stored in the Simulationarchive.
This allows you to get reproducible random number even after restarting a simulation.
* Random numbers generated with the `reb_rand_*()` functions were not thread-safe.
They are thread-safe now. Note that this required an API change. All `reb_rand_*()`
functions now require the simulation structure as an argument. This is because the
random number generator seed is now stored in the simulation structure.

* Correct handling of test particles in reb_transformations.
* Small bug fixes

* WHFast: Fixes multiple issues with testparticles in WHFast.