GenericGraph extended to a full-fledged graph

It now implements edge list, bidirectional adjacency list, and bidirectional incidence list. (all interface functions are tested)
some extension of the constructing functions
updated doc for v0.3
correct URL of the Travis logo
Enable release and nightlies tests on travis
Merge pull request #55 from aviks/as/travis

Enable release and nightlies tests on travis
fixed deprecation warnings caused by new Set syntax
fix error caused by wrong field call
Merge pull request #57 from lpand/master

fix error caused by wrong field call inside getindex of TargetIterator
fix another wrong field bug