Return raw SOS response if no Exception tag is found.  #97.
Follow the SOS spec and use case sensitive observedProperty as a key.

fixes #97
Add helper to SensorML capabilities element. Cleanup.
Make the python-dateutil requirement >=
Fixes #100 - for cases when CSW nextRecord is missing.
Merge pull request #101 from datagovuk/100-nextrecord

Fixes #100 - for cases when CSW nextRecord is missing.
Merge pull request #99 from asascience-open/master

SOS fixes and add a SensorML parsing helper