NAME:
  edgefit
 PURPOSE:
  Fit an edge between two signal levels
 DESCRIPTION:
 CATEGORY:
  Function fitting
 CALLING SEQUENCE:
  edgefit,x,y
 INPUTS:
  x - independent variable (vector)
  y - dependent variable (vector)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  Two plots are generated and the fitted values are printed to the screen.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  96/12/23, Written by Marc W. Buie, Lowell Observatory