Added support for "A3" autotiles, bugfixes

Just wanted to do a quick update.

First, I've added support for "A3" tilesets via two new drag-and-drop targets to autotile-packing-tools:

• unpack-minitile-a3.cmd
• unpack-minitile-a3-gms16.cmd 

These work just like the "A2" versions, unpacking for both tiled and GameMaker Studio.

Second, I've fixed a few bugs around path handling, so the .cmd files no longer need to be in the same folder as the images you are unpacking.

Lastly, I've tweaked the .cmd files to make it easier to use this tool on autotiles that are larger than 16x16.  If you are working with 32px/HD tiles, simply open the .cmd file you want to use in any text editor (e.g., vscode or notepad) and change the part that says:

--minitile-size 8

to

--minitile-size 16

The number value should be equal to the width of your tile, divided by the 2.

Happy unpacking!