BIG UPDATE: big tiled image, lots of appearance options!

Added the final tiling of all the images into a large table, and a lot
of related appearance options: box sizes, padding, background color,
font color, font size, etc.

Moved the run_command_get_output function lower; re-ordered the
constants.
Made the default color-tile folder be based on an envirnmental variable,
instead of a hardcoded path just for my own use; changed argument
parsing to implement that.  Tested, works with an environmental variable
for me.

Changed all instances of building paths by hand (as 'folder/file') to
the proper OS-independent os.path.join.

Implemented updating existing folders (normally skip files that already
exist, make new ones as needed and delete old unneeded ones; if desired,
regenerate all).

Implemented option to not stretch the image tiles (just have some rows
shorter than others, if there are e.g. 2 possible secondary colors and
10 primary and tertiary).

Rewrote docstring.

I tested everything, and it seems to work.

Changes to example_input.txt:
 - changed dragon names in to better demonstrate allowed characters.
 - changed spacing/etc for better illustration
 - removed one dragon, to get different male/female numbers

Regenerated example-output to reflect all these changes.