GetViewerList Extract the list of file formats, viewers and full viewer commands from the typedef array
Argument list: <format> <viewerVar> <viewercmdVar>
The definitions have been read from the etc/types.def file into the typedef array. This procedure reformats the information as lists which are easier to handle.
format Output list of supported file formats
viewer Output list of viewer names (corresponding to format list) which is the name of the viewer as seen by the user
viewercmd Output list of the commands required to run viewers (corresponding to format and viewer lists)