Added subset of unifont hexadecimal font to texttopng

Unifont is a little bigger in dimensions so more useful for me out of the box with pypng.
I haven't modified the existing code or added command line options for this new font so I'll leave that to you.

Here's the Unifont Info. It's a full unicode character set so quite large. I created a subset for simplicity.

GNU Unifont created by Roman Czyborra

http://czyborra.com/unifont/