Xcompact3d-toolbox

Fixed

- Fixed bug producing potential `KeyError` on the cylinder geometry

Changed

- `param = {'mytype': np.float64}` changed to just `mytype = float64` ([param.py](xcompact3d_toolbox\param.py)), by [fschuch](https://github.com/fschuch).
- Code style changed to [black](https://github.com/psf/black), by [fschuch](https://github.com/fschuch).

Documentation

- Created the `docs` folder powered by [sphinx](https://github.com/sphinx-doc/sphinx), by [fschuch](https://github.com/fschuch).
- Examples for Sandbox flow configuration (by [fschuch](https://github.com/fschuch)):
- [Turbidity Current in Axisymmetric Configuration](docs\examples\Axisymmetric_flow.ipynb);
- [Flow Around a Complex Body](docs\examples\Cylinder.ipynb).
- Tutorials (by [fschuch](https://github.com/fschuch)):
- [Parameters](docs\tutorial\parameters.ipynb).
- Added a page for autogenerated API references, by [fschuch](https://github.com/fschuch).
- Extended the docstring for most classes, methods, and functions, by [fschuch](https://github.com/fschuch).
- Integration with [Read the Docs](https://xcompact3d-toolbox.readthedocs.io/en/latest/), by [fschuch](https://github.com/fschuch).

Internals

- [python-versioneer](https://github.com/warner/python-versioneer) removed the tedious and error-prone "update the embedded version string" step from our release process, by [fschuch](https://github.com/fschuch).

The kickoff for the project, the first release to PyPi.

Added

- CHANGELOG.md by [fschuch](https://github.com/fschuch).
- `class Parameters` built on top of [traitlets](https://traitlets.readthedocs.io/en/stable/index.html), for type checking, dynamically calculated default values, and "on change" callbacks, by [fschuch](https://github.com/fschuch).
- [ipywidgets](https://ipywidgets.readthedocs.io/en/latest/) for all relevant parameters and two-ways linking with [traitlets](https://traitlets.readthedocs.io/en/stable/index.html) variables, by [fschuch](https://github.com/fschuch).
- Accessors for [xarray](http://xarray.pydata.org/en/stable/)'s `Dataset` and `DataArray`, making possible high-order derivatives (with appropriated boundary conditions), I/O, parallel execution with pencil decomposition (powered by [dask](https://dask.org/)) and integration with `scipy.integrate.simps` and `scipy.integrate.cumtrapz`. By [fschuch](https://github.com/fschuch).
- Ported genepsi.f90 to genepsi.py (powered by [Numba](http://numba.pydata.org/)), generating all the files necessary for our customized Immersed Boundary Method, by [fschuch](https://github.com/fschuch).
- Support to *Sandbox Flow Configuration* (see [fschuch/Xcompact3d](https://github.com/fschuch/Xcompact3d/)), by [fschuch](https://github.com/fschuch).
- Ahmed body as benchmark geometry, mirror and plotting tools, by [momba98](https://github.com/momba98).