+Restructured the SIS2 directory & added LICENSE.md

  Changed the SIS2 directory structure to follow the pattern used by MOM6, by
adding two new sub-directories, src and config_src, with two different versions
of SIS2_memory.h available via config_src directories.  In addition a new
LICENSE.md file with the full GNU version 3 license for SIS2.  All answers are
bitwise identical, but this may require some modifications to compile scripts.

config_src/dynamic_symmetric/SIS2_memory.h

@@ -0,0 +1,58 @@
+!********+*********+*********+*********+*********+*********+*********+*
+!*   This include file determines the compile-time memory settings    *
+!*  for the Sea Ice Simulator (SIS), versions 2 and later.            *
+!********+*********+*********+*********+*********+*********+*********+*
+
+!  Specify the numerical domain.
+#define NIGLOBAL_ NONSENSE_NIGLOBAL
+#define NJGLOBAL_ NONSENSE_NJGLOBAL
+                               !    NIGLOBAL_ and NJGLOBAL_ are the number of thickness
+                               !  grid points in the zonal and meridional
+                               !  directions of the physical domain.
+#define NK_ NONSENSE_NK
+                               !    The number of layers in the ocean.
+#define NCAT_ICE_ NONSENSE_NCAT
+                               !    The number of sea-ice categories.  When
+                               !  open water is considered, there are 0:NCAT_ICE
+                               !  categories in total.
+#define NK_ICE_  NONSENSE_NK_ICE
+                               !    The number of vertical partitions within the
+                               !  sea-ice.  (For SIS this is 2; for SIS5L it is 4.)
+#define NK_SNOW_ NONSENSE_NK_SNOW
+                               !    The number of vertical partitions within the
+                               !  snow layer atop the sea-ice, usually 1.
+#undef STATIC_MEMORY_
+                               !    If STATIC_MEMORY_ is defined, the principle
+                               !  variables will have sizes that are statically
+                               !  determined at compile time.  Otherwise the
+                               !  sizes are not determined until run time. The
+                               !  STATIC option is substantially faster, but
+                               !  does not allow the PE count to be changed at
+                               !  run time.
+#define SYMMETRIC_MEMORY_
+                               !    If defined, the velocity point data domain
+                               !  includes every face of the thickness points.
+                               !  In other words, some arrays are larger than
+                               !  others, depending on where they are on the 
+                               !  staggered grid.
+
+#define NIPROC_ NONSENSE_NIPROC
+                               !    NIPROC_ is the number of processors in the
+                               !  x-direction.
+#define NJPROC_ NONSENSE_NJPROC
+                               !    NJPROC_ is the number of processors in the
+                               !  y-direction.
+
+#define MAX_FIELDS_ 50
+                               !    The maximum permitted number (each) of
+                               !  restart variables, time derivatives, etc.
+                               !  This is mostly used for the size of pointer
+                               !  arrays, so it should be set generously.
+
+#define NIHALO_ 2
+#define NJHALO_ 2
+                               !   NIHALO_ and NJHALO_ are the sizes of the
+                               ! memory halos on each side.
+
+#include <MOM_memory_macros.h>
+#include <SIS_memory_macros.h>