Add format usable by endomondo.com

```
I tried your tool, and it worked great. However, I am also a user of endomondo, 
and they do not support the .gnm-format. Would it be an idea to support the 
.gpx and .tcx format also?

-- 
Lars Olesen
motionsplan.dk
```

Original issue reported on code.google.com by `lsole...@gmail.com` on 25 Jun 2010 at 5:24
