Added some thoughts about grid variable implementation.
Forgot to commit the updates to the grid_variables notes file before splitting
the branch, so moving it in now.
Created file Support.hpp for general support values/functions that may be used
throughout the code.  Added a DelayedConst template class to Support.hpp.
Created a test directory; moved test_array.cpp there and added
test/delayedconst.cpp.  Started working on the new GridVar.cpp.
Changed Driver and Grid to use DelayedConst variables.  Implemented grid
variables Grid::CellVar and Grid::FaceVar (but not yet changed the Grid over to
using them in place of the Array class).
Modified the program to use the new GridVars (CellVar and FaceVar) in place of
the old Arrays.
Minor edit.
Merge branch 'gridvar'
- Replace Array with CellVar and FaceVar, which are bound to the Grid sizing
- Adds the DelayedConst, a variable that can be set once and only once