Break up larger source code files

[tlnagy]

Several of the files are getting unwieldy in size, especially statistics.jl, guide.jl, and Gadfly.jl. I think it would make sense to break these up like what was done for Geoms. Thoughts?

 $ find . -name '*.jl' -type f | xargs wc -l

     415 ./aesthetics.jl
     277 ./bincount.jl
      81 ./color_misc.jl
     277 ./coord.jl
      83 ./data.jl
    1238 ./Gadfly.jl
     284 ./geom/bar.jl
     142 ./geom/beeswarm.jl
     138 ./geom/boxplot.jl
     129 ./geom/errorbar.jl
      41 ./geom/hexbin.jl
     166 ./geom/hvabline.jl
     293 ./geom/label.jl
     195 ./geom/line.jl
      56 ./geom/point.jl
     100 ./geom/polygon.jl
      96 ./geom/rectbin.jl
      72 ./geom/ribbon.jl
      90 ./geom/segment.jl
     379 ./geom/subplot.jl
      40 ./geom/violin.jl
      70 ./geometry.jl
    1193 ./guide.jl
     325 ./mapping.jl
     418 ./misc.jl
      12 ./open_file.jl
     199 ./poetry.jl
     674 ./scale.jl
     219 ./shapes.jl
    1892 ./statistics.jl
     378 ./theme.jl
     327 ./ticks.jl
      60 ./varset.jl
   10359 total

[Mattriks]

I've started doing this for Guides in #1156

[tlnagy]

Awesome. It looks like guide.jl and statistics.jl are the worst offenders.

[bjarthur]

i'd hold off on partitioning guide.jl and statistics.jl until #1116 is merged as fixing the conflicts would be more difficult.