A. Goodman, A. Pepe, A. Blocker, C. Borgman, K. Cranmer, M. Crosas, R. Di Stefano, Y. Gil, P. Groth, M. Hedstrom and 5 other author(s). (2014)cite arxiv:1401.2134Comment: Accepted in PLOS Computational Biology. This paper was written collaboratively, on the web, in the open, using Authorea. The living version of this article, which includes sources and history, is available at http://www.authorea.com/3410/.