improve docstrings in Graph class
improve docstrings in Graph class

--HG--
extra : convert_revision : svn%3A3ed01bd8-26fb-0310-9e4c-ca1a4053419f/networkx/trunk%40900

chrisnatali/networkx,jtorrents/networkx,kai5263499/networkx,jfinkels/networkx,bzero/networkx,RMKD/networkx,aureooms/networkx,debsankha/networkx,wasade/networkx,tmilicic/networkx,debsankha/networkx,jakevdp/networkx,dhimmel/networkx,harlowja/networkx,RMKD/networkx,harlowja/networkx,beni55/networkx,cmtm/networkx,goulu/networkx,Sixshaman/networkx,nathania/networkx,kai5263499/networkx,blublud/networkx,SanketDG/networkx,farhaanbukhsh/networkx,jakevdp/networkx,jtorrents/networkx,kai5263499/networkx,kernc/networkx,jcurbelo/networkx,chrisnatali/networkx,dhimmel/networkx,NvanAdrichem/networkx,ionanrozenfeld/networkx,jni/networkx,farhaanbukhsh/networkx,dmoliveira/networkx,sharifulgeo/networkx,ghdk/networkx,nathania/networkx,ionanrozenfeld/networkx,nathania/networkx,kernc/networkx,farhaanbukhsh/networkx,aureooms/networkx,OrkoHunter/networkx,ghdk/networkx,bzero/networkx,jni/networkx,dmoliveira/networkx,JamesClough/networkx,ltiao/networkx,blublud/networkx,andnovar/networkx,sharifulgeo/networkx,chrisnatali/networkx,ionanrozenfeld/networkx,harlowja/networkx,dmoliveira/networkx,debsankha/networkx,yashu-seth/networkx,dhimmel/networkx,kernc/networkx,bzero/networkx,jni/networkx,jakevdp/networkx,michaelpacer/networkx,blublud/networkx,sharifulgeo/networkx,RMKD/networkx,ghdk/networkx,aureooms/networkx