GPX parsing should be much better now.

The parser now looks at the first track point to get an idea of what values are inside,
no longer hardcoded to lat,lon,time,name

The following
```xml
<trkpt lon="-71.72464708797634" lat="42.43801748380065">
  <ele>147.60000610351562</ele>
  <time>2013-09-28T17:34:13.000Z</time>
</trkpt>
```
would yeild a csv that looks like 
```
lon,lat,ele,time
-71.72464708797634,42.43801748380065,147.60000610351562,2013-09-28T17:34:13.000Z
```