More variants for the station input are tested.
Added a StationXML test file.
Added tests for the StationXML helper
Adding StationXML helper
Added test for adding StationXML files
Added ability to download arbitrary data from URLs.

Additionally some slight refactoring.
Added proper StationXML support
Adding example SAC file.
Adding test for SAC files.
Improvements to the SAC parsing.
Adjust SAC test for floating point rounding errors
Adding tests for some other possible sac files.

Makes the whole thing more robust.