k9an decoder now decodes wspr15 mode

The latest version (github.com/k9an/wsprcan) decodes both wspr2 and wspr15 files. It will auto detect the mode with a .c2 file. To decode a 15-minute .wav file, use the -m option. I have tested this on exactly 3 cases, so I'd appreciate feedback from anyone who tries the wspr15 mode.

Steve, k9an