Things to Do:
-------------

    Help Page:
done	- examples showing image operand usage
done	- examples of zscale/grey/bscale/gamma funcs in complex exprs

done	- clean up output header description
done	- verbose is used as terminal output and raw header flag - change
done	- define 'composite' in interleave description
	- format=raw for >3-D images, more detail
done?	- clean up description of image list handling for large groups of
	  images - perhaps multiple params for operands
done	- format should be a query param
???	- should 'outbands' be 'outexpr'
???	- should there be an 'append' param to append existing files
done	- what happens if 3-D image passes in for builtin conversion
done	- Dave's typos/comments
	- note that grouping exprs in function may affect the number of
	  perceived expressions, e.g.  "psdpi ( (b1, b2, b3), 150.0)"
done	- add block() function to help page
done	- add setcmap() function - this is what's currently defined as the
	  setlut() function.
???	- Clear up confusion about LUT and colormaps in the help page

    Source:
done	- block() function fills full height of expression, not just that
	  height specified 
done	- remove constraint on image sizes all being equal
done	- @param and tag.param operators need to be implemented
done	- text output still needs work
done	- remove xvv_initop() calls - interface violation
done	- finish header output
done	- is zscale() mapping the pixels NOT in the range 0-255 for gif???
done	- need to implement XWD
	- need to patch xwd expr for RGB to add alpha channel
	- optimize image reads from 3D images