added graph4scala dependency
replaced allNodes with an implementation based on Graph4Scala
changed to mutable Graph, cause the immutable is so slow I first thought I got stuck in an endless loop
changed implementation of connectionsOf to Graph4Scala

added some self tests to AnalyzerTest
added a test with multiple connections to GraphTest
fixed a typo in WriterTest
also fixed the broken allNodes implementation
removed _edges member
replaced contentsOf implementation with an implementation based on Graph4Scala
removed the -contents field

also did some realy minor refactorings
extracted duplicated code
Merge branch 'master' of github.com:schauder/degraph