code: public static String gridAsString(String hash, int size, Set<String> highlightThese) {
          return gridAsString(hash, -size, -size, size, size, highlightThese);
      }
docs: <p>
  Returns a String of lines of hashes to represent the relative positions
  of hashes on a map. The grid is of height and width 2*size centred around
  the given hash. Highlighted hashes are displayed in upper case. For
  example, gridToString("dr",1,Collections.&lt;String&gt;emptySet()) returns:
  </p>
  
  <pre>
  f0 f2 f8
  dp dr dx
  dn dq dw
  </pre>
  
  @param hash central hash
  @param size size of square grid in hashes
  @param highlightThese hashes to highlight
  @return String representation of grid