Add support for 'advertised' property to layer and featuretype
Added a default True value for 'advertised' property since the property is not always present in REST API representations
Revert back without default for 'advertised'; will not work that way.   Intsead check for None value for 'advertised' property
Merge pull request #35 from mwengren/featuretype_advertised

Add support for 'advertised' property of FeatureType, Coverage, and Layer classes.