Turn merkledag.Node into an interface#3301

Merged

whyrusleeping merged 2 commits intomasterfrom feat/node-interface

Oct 17, 2016

+901-612

Commits on Oct 12, 2016

merkledag: change 'Node' to be an interface
whyrusleeping
committed

Commits on Oct 14, 2016

extract node interface
whyrusleeping
committed