Split documentation into smaller chunks

[mccalluc]

Follow up for #70

   Non-genomic raster data
   Genomic data
      Bed Files
      Bedpe-like Files
      BedGraph files
      bigWig files
      Chromosome Sizes
      Gene Annotation Tracks
      Hitile files
      Cooler files
      Multivec Files (Maybe multivec is a single page?)
         Epilogos Data (multivec)
         States Data (multivec)
         Other Data (multivec)