N4 create richer SDcard image

[nealcrook]

Create SDcard image with better set of PolyDos and CP/M disk images.

[nealcrook]

Added PolyDos disk images as virtual disks 4,5,6,7,8,9 to latest nascom4_sdcard.img

[nealcrook]

.. but I did not expand those images to make them as large as they could be.. that could be a new option for sdcard_editor tool

[nealcrook]

Ha! the image size is actually coded in the "bios" ROM and so a sub-sized image put on SDcard at the correct origin (as these all are) will automatically be considered as large as they can be. No mods needed.