Use indices in testing whether on
a boundary. This is done to avoid using the upper and lower coordinate extents
in this check as floats equality comparison is not safe."
initial hacking to add flags for boundaries
add flags to the grid and dimension
objects to indicate whether the grid is on boundary
use on_lower_boundaries and on_upper_boundaries grid
flags in the methods apply_q_bcs and apply_aux_bcs instead of
making indices comparison
correct spelling error
Merge pull request #220 from amal-ghamdi/add_bc_flags

solution for issue #154, adding boundary flags