Add sphinx docs for data watching API.
Add sphinx docs for data watching API.

python-zk/kazoo,rockerbox/kazoo,pombredanne/kazoo,harlowja/kazoo,bsanders/kazoo,rackerlabs/kazoo,tempbottle/kazoo,Asana/kazoo,jacksontj/kazoo,max0d41/kazoo,python-zk/kazoo,bsanders/kazoo,AlexanderplUs/kazoo,rgs1/kazoo,kormat/kazoo,rackerlabs/kazoo,max0d41/kazoo,tempbottle/kazoo,kormat/kazoo,pombredanne/kazoo,rockerbox/kazoo,jacksontj/kazoo,rgs1/kazoo,AlexanderplUs/kazoo,harlowja/kazoo