Chart: Port to lens

Most of these changes were just flipping around underscores. This was
mostly accomplished by,

  %s/\([a-zA-Z0-9_]+\)_\([^a-zA-Z0-9]\)/_\1\2/c
chart-cairo: Port to lens
chart-diagrams: Port to lens
Renderable: Use makeLenses to create lenses
chart-tests: Port to lens
chart: Update comments and documentation for lens
Add lower bounds on lens
Merge pull request #2 from bgamari/lens

Port to lens