daviddritschel/Hydra: Version 1.0.0

This is the first release of Hydra, originally devised and developed by David Dritschel in 1993. Hydra is a general purpose software package for simulating idealised geophysical (atmospheric/oceanic) and astrophysical (MHD) systems in a variety of geometries (periodic, semi-periodic, rectangular, spherical) using "Contour Advection", a numerical method originally developed by D G Dritschel and M H P Ambaum in the Quarterly Journal of the Royal Meteorological Society, volume 123, pages 1097 - 1130 (1997). Contour Advection grew out of Contour Dynamics and Contour Surgery, the latter developed by D G Dritschel in the Journal of Computational Physics, volume 77, pages 240 - 266 (1988). See also the webpage held at the University of St Andrews, https://risweb.st-andrews.ac.uk/portal/en/persons/david-gerard-dritschel(5891c03b-9bb7-4713-bebe-a0c0f243f605).html, or search "David Dritschel University of St Andrews" for a complete listing of papers related to Contour Advection.