Added Rubydora::Datastream#empty?
Rubydora::Datastream#has_content? returns true if controlGroup is 'M'
Merge pull request #58 from dchandekstark/datastream-empty

Added Rubydora::Datastream#empty?
Merge pull request #59 from dchandekstark/patch-has-content

Rubydora::Datastream#has_content? returns true if controlGroup is 'M'