Added minimal StationXML test file
Started implementing reading and writing StationXML files.
Reading and writing the minimal StationXML works.

Implemented the basic structure for reading and writing to and from
inventory objects.
Fixing inventory test.
Added writing of ObsPy module tags to StationXML.
Added test for reading other module tags.
Added test for reading and writing the full root element.
Added new test file.

This file has one fully fledged station.
Started to implement reading of the full network file.

Also added parts of a new Comment object.
Added Comment class.
Reading and writing a fully filled network works.
Added station count field to the network.
Refactoring.

Put functionality to read/write the base node type in their own
functions. Will ease it for the other types.
Added new Site object.
Adding test file with all station information.
Merge branch 'master' into obspy.station
Making the station example file more complex.
Reading stations works.
Implemented XML comparision helper function.
Writing station tag works.