Parcels

1. Improved advection-diffusion kernels, as detailed in [this tutorial](https://nbviewer.jupyter.org/github/OceanParcels/parcels/blob/master/parcels/examples/tutorial_diffusion.ipynb) by daanreijnders (#823)
2. Support for time-evolving sigma-grids (660)
3. New interpolation scheme for tracers near coastlines, as detailed in [this tutorial](https://nbviewer.jupyter.org/github/OceanParcels/parcels/blob/master/parcels/examples/tutorial_interpolation.ipynb), thanks to pierrick-giffard. (#815)
4. Addition of Kernels to calculate the TEOS-10 equation of state, thanks to pdnooteboom (816)
5. Partial implementation of AnalyticalAdvection Kernel following [Döös et al 2017](https://www.geosci-model-dev.net/10/1733/2017/), see also [this tutorial](https://nbviewer.jupyter.org/github/OceanParcels/parcels/blob/master/parcels/examples/tutorial_analyticaladvection.ipynb)
6. Support for dimensions of length-1. This greatly simplifies creating FieldSets that are constant in longitude and/or latitude (817)

Plus a large number of minor bug fixes

1. Speed up by perhaps a factor 10(!) in some use-cases by switching data structure of `ParticleSet` from Array-of-Structures to Structure-of-Arrays (678, thanks angus-g!)
2. Support for sigma-grids with time-varying depth dimensions (660, see also [this tutorial](https://github.com/OceanParcels/parcels/blob/master/parcels/examples/tutorial_timevaryingdepthdimensions.ipynb))
3. Further fixes some issues with `dask` chunking ( 764, 774, 776)
4. Improves reliability when `dt` is very small (< 0.001 s) (762)
5. Support for a new ErrorCode `StopExecution` (780)
6. Support for python3.8 (753)

And various other minor bug fixes

1. It fixes some Issues with dask chunking, particularly in 3D simulations (738, 740 and 731)
2. It adds a von Mises distribution to `parcels.random` (725)

And numerous smaller bugfixes.

1) It fixes some serious issues with memory usage for field chunking (see 668, 703 and 711), which have now been addressed in 719
2) Fixing xarray compatibility (716)
3) Fixing a bug in cartopy.quiver (714)
4) New kernels to compute density (688)

And various other minor bug fixes

1. It fixes a serious bug on some systems with floating point accuracy, that could lead to incorrect output files (see 670 and solution at 672). For this reason, all users are encouraged to use this new version v2.1.2 instead of v2.1.1.
2. It also fixes a smaller bug (676) with the `timestamps` argument in `Field.from_netcdf()`