shp2img command line documentation (usage message)

[jidanni@…]

Below, my comments have ">", and Warmerdam's reply doesn't.
I'm not sure if he implemented all my ideas.

> $ shp2img
> Say:
> Syntax: shp2img -m mapfile [-o image] [-e minx miny maxx maxy]
>                 [-l "layer1[ layer2]..."] [-i format]
> [Note I have changed all both lines]
> Else also no one will ever know how to add more than one layer and
> will try commas. Also -l NON_EXISTENT doesn't raise an error.
> Also besides just syntax, it should say Purpose: ... as there is no
> man page. Same for its sibling programs.
> Also add options to turn off layers.

I have updated the docs for -l.  I never would have guessed it works as it
does.  There is some sort of documentation for the utilities on the MapServer
plone site.