#40 add .bpng support

[Ricardo Quesada]

Hi,
I'm not sure what is the standard format to for the
bughouse games.
I found this page: http://cashton.homeip.net/ubd/
and the games are all in this .bpng format, which is
very similar to .pgn but eboard doen't support it :-(

[Felipe Bergo]

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will be done...some day...