NAME:
    sshift2d
 PURPOSE: (one line)
    Shift a 2-D array using a damped sinc function for the fractional part.
 DESCRIPTION:

 CATEGORY:
    Mathematical
 CALLING SeqUENCE:
    result = sshift2d( array, shiftvec )
 INPUTS:
    array    : Array to be shifted.
    shiftvec : Vector of two elements: [ xshift, yshift ].
 OPTIONAL INPUT PARAMETERS:

 KEYWORD PARAMETERS:
     EDGE_ZERO: Flag, if set will force the wrapped edges to zero.
     
 OUTPUTS:
    The shifted array is returned as the function value.
 COMMON BLOCKS:

 SIDE EFFECTS:

 RESTRICTIONS:

 PROCEDURE:

 MODifICATION HISTORY:
    February, 1993:
    Copied from "sincshift.pro" written by John Spencer, Lowell Observatory.
    Very minor modifications by Doug Loucks, Lowell Observatory.
    2010/05/01, Florian Scheulen, Harvey Mudd College, added EDGE_ZERO keyword
    2010/05/05, MWB, style editing.
    2018/02/19, MWB, fixed shiftrep to make keyword optional