Additional information passed in as table options

The CCTK_InterpLocalUniform() API accepts a table handle as one of its arguments which can be used to pass additional information to the local interpolator via table options.

The only table option supported so far by LocalInterp's "uniform cartesian" operator is the interpolation order which must be passed as a CCTK_INT value with key "order". Options with keys "N_boundary_points_to_omit", "boundary_off_centering_tolerance", or "boundary_extrapolation_tolerance" (which are usually passed by a global interpolator) are also recognized but silently ignored (a level-4 warning message will be issued in this case).