This directory presents a template for new Unit development in FLASH 3.
The directory heirarchy reflects FLASH 3 architecture, and so
do the individual files. 

Each subdirectory in this template has its own README file which documents
the functions/rules that apply to that level. 

The top level (current) directory contains subunits and stubs or null
implementations for all the routines in unit "MyUnit" that are
public, and can be called from outside the module. The division of a
unit into subunits is based upon identifying self-contained subsets of
its public interface (API). A subunit implements at least one
routine of the unit's API, and no two subunits implement the same
API function. Every unit has at least one subunit "MyUnitMain",
and a function in its API, MyUnit_init.F90 to
initialize the unit and some MyUnit.F90 that implements the 
solver in the module. There may be more subunits and API functions
depending upon the complexity of the unit. There should
be one file for every public function of the unit. The only other files that
are allowed to exist at this level are MyUnit.h and
MyUnit_interface.h, if they are needed. MyUnit_interface.h includes
interface definitions and MyUnit.h includes constants that
MyUnit wants to make public. Interfaces must be defined for
functions that either have optional arguments, or pass pointers as 
arguments. MyUnit_foo2 in this template is an example of a
function that passes a pointer, and hence has an interface.

The stubs or null implementations completely ignore all input
arguments of the function, and initialize the "output only" arguments
with some valid default value. Thus these functions return without
making any difference to the state of the run, except making sure that
NaN's are not returned in output arguments. This mechanism permits an
application to exclude the unit without having to modify the code
that calls the API of this module. This functionality has always been
there in FLASH2, it is clarified in FLASH3. 

The example of documentation is included in all the files that have
stubs of the public functions in this top level directory.