kml export

This pull request adds support to export log files to .kml files for display in google earth

* The source for the position data can be specified via --source argument (GPOS or GPS)
* The lines are colored according to MainState of the vehicle
* Only .bin (DataFlash) log-files are supported, I am happy about suggestions how to include support for other files
* kml is generated using https://code.google.com/p/simplekml/