title: documenting dataset with roxygen2
body: <p>I'm trying to document some datasets in an R package using roxygen2. Considering just one of these:</p>
  
  <ul>
  <li>I have <code>mypkg/data/CpG.human.GRCh37.RDa</code></li>
  <li>which contains an object called <code>CpG.human.GRCh37</code></li>
  <li><p>and a file called: <code>mypkg/R/cpg-data.R</code>, which contains:</p>
  
  <pre><code>#' @name CpG.human.GRCh37
  #' @title CpG islands - human - genome build: GRCh37/hg19
  #' @description This data set list the genomic locations of human CpG islands,
  #' with coordinates based on the GRCh37 / hg19 genome build.
  #' @docType data
  #' @usage CpG.human.GRCh37
  #' @format a \code{RangedData} instance, 1 row per CpG island.
  #' @source UCSC Table Browser
  #' @author Mark Cowley, 2012-03-05
  #' @export
  NULL
  </code></pre></li>
  </ul>
  
  <p>When I roxygenize, this gets created <code>mypkg/man/CpG.human.GRCh37.Rd</code>, containing:</p>
  
  <pre><code>    \docType{data}
      \name{CpG.human.GRCh37}
      \alias{CpG.human.GRCh37}
      \title{CpG islands - human - genome build: GRCh37/hg19}
      \format{a \code{RangedData} instance, 1 row per CpG island.}
      \source{
        UCSC Table Browser
      }
      \description{
        This data set list the genomic locations of human CpG
        islands, with coordinates based on the GRCh37 / hg19
        genome build.
      }
      \author{
        Mark Cowley, 2012-03-05
      }
      \usage{CpG.human.GRCh37}
      \keyword{datasets}
  </code></pre>
  
  <p>and <code>export(CpG.human.GRCh37)</code> gets added the <code>NAMESPACE</code> file.</p>
  
  <p>but when I <code>R CMD CHECK</code> I get:</p>
  
  <pre><code>...
  ** testing if installed package can be loaded
  Error in namespaceExport(ns, exports) : 
    undefined exports: CpG.human.GRCh37
  Error: loading failed
  ...
  </code></pre>
  
  <p>Nowhere have I told R where to find this dataset, though I would assume that the <code>mypkg/data/&lt;name&gt;.RDa</code> would be a good first guess.
  Any hints would be awesome.</p>
  
  <p>If Hadley's watching, I notice that an \usage section is not created and the @usage directive is ignored.</p>
  
  <p>i'm using roxygen-2.2.2, on R 2.13.1</p>