Add OTU generation references

Here are some more references on OTU generation that you could cite at the same time as the CROP paper (Hao et al, 2011).

(in amsrefs format since that's what I use)

\bib{CWC12}{article}{
   author = {Cheng, Lu},
   author = {Walker, Alan W.},
   author = {Corander, Jukka},
    title = {Bayesian estimation of bacterial community composition from 454
             sequencing data},
  journal = {Nucleic Acids Research},
   volume = {40},
   number = {12},
     date = {2012},
    pages = {5240--5249},
      doi = {10.1093/nar/gks227},
}

\bib{KS10}{article}{
   author = {Kelley, David R.},
   author = {Salzberg, Steven L.},
    title = {Clustering metagenomic sequences with interpolated Markov models},
  journal = {BMC Bioinformatics},
   volume = {11},
   number = {544},
     date = {2010},
      doi = {10.1186/1471-2105-11-544},
}

\bib{WYS13}{article}{
   author = {Wang, Xiaoyu},
   author = {Yao, Jin},
   author = {Sun, Yijun},
   author = {Mai, Volker},
    title = {M-pick, a modularity-based method for OTU picking of 16S rRNA
             sequences},
  journal = {BMC Bioinformatics},
   volume = {14},
   number = {43},
     date = {2013},
      doi = {10.1186/1471-2105-14-43},
}

matsen / sbreview

Add OTU generation references #4