adding network module
adding network module

spreg-git/pysal,sjsrey/pysal_core,dfolch/pysal,sjsrey/pysal,chhao91/pysal,lixun910/pysal,sjsrey/pysal_core,schmidtc/pysal,jlaura/pysal,pysal/pysal,pedrovma/pysal,nathania/pysal,pastephens/pysal,ljwolf/pysal_core,schmidtc/pysal,darribas/pysal,lixun910/pysal,badjr/pysal,TaylorOshan/pysal,TaylorOshan/pysal,nathania/pysal,ljwolf/pysal,sjsrey/pysal_core,TaylorOshan/pysal,ljwolf/pysal_core,chhao91/pysal,jlaura/pysal,jlaura/pysal,dfolch/pysal,badjr/pysal,pastephens/pysal,spreg-git/pysal,weikang9009/pysal,hasecbinusr/pysal,hasecbinusr/pysal,pastephens/pysal,lanselin/pysal,ljwolf/pysal_core,hasecbinusr/pysal,darribas/pysal,ljwolf/pysal,ljwolf/pysal,lixun910/pysal