Added a StationXML file including availability.
Read support for availability information.

Includes a test.
Write support for StationXML availability tags.
ChangeLog
Support for the matchtimeseries parameter.

Introduced in the FDSNWS 1.1 specification.
Changelog for the FDSNWS changes.
Fixing all FDSN tests...
Documentation of the matchtimeseries parameter.
Fixing typos.
Merge pull request #853 from krischer/stationxml_availability

Read/Write support for the DataAvailability tag in StationXML and update to FDSN WS 1.1
adding obspy.ah to docs