NAME:
  htmltcell
 PURPOSE:   (one line only)
  Format a single cell of information for an html table
 DESCRIPTION:
 CATEGORY:
  Miscellaneous
 CALLING SEQUENCE:
   str = htmltcell(tstr)
 INPUTS:
  tstr - String that is the visible content of a cell
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  CENTER - Flag, if set makes field centered
  URL    - String, if provided will be setup as a hyperlink for the
             contents of the cell
 OUTPUTS:
  Return value is the string that encodes all the formatting requests
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2024/11/09