added feature expressions diffs:
whenever a feature needs to be converted to a CExpr we diff the context 1 level above the feature and the feature

added a new data structure which indicates if we need a second rerun of ifdeftoif because of usages which occur before their declarations

added getClauses for feature model

added a method which generates an option struct from a feature model

added a method which generates an initialize function from a dimacs file
Merge remote-tracking branch 'origin/master'