. Author manuscript; available in PMC: 2017 Aug 15.
Published in final edited form as: Nat Methods. 2016 Oct 31;13(12):1036–1042. doi: 10.1038/nmeth.4038
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests. Readers are welcome to comment on the online version of the paper. Correspondence and requests for materials should be addressed to M.C.B. (bassik@stanford.edu)