Reorganize methods in vfg.py, and add some comments
Reorganize methods in vfg.py, and add some comments

schieb/angr,schieb/angr,haylesr/angr,tyb0807/angr,angr/angr,angr/angr,f-prettyland/angr,chubbymaggie/angr,axt/angr,iamahuman/angr,schieb/angr,iamahuman/angr,f-prettyland/angr,tyb0807/angr,iamahuman/angr,axt/angr,chubbymaggie/angr,haylesr/angr,f-prettyland/angr,axt/angr,angr/angr,chubbymaggie/angr,tyb0807/angr