moved assertCard and assertCardSet to Cards so they can be used in all tests
added assertRenderModel, and put context messages in the subfield assertions of assertCard and assertCardSet
created CompoundImage for treating groups of ImageAssets as a single unit when rendering
updated CompoundRenderable refs to CompoundImage
set to use assertRenderModel instead of assertEquals, for easier failure identification
added grouping of ImageAssets w/in the body into CompoundImage wrappers so they can be flowed into the body as a unit without as much mumbo-jumbo.
renamed CompoundImage to CompoundImageAsset
removed the line/index stuff from RenderContext, along with the stuff in render(ImageAsset) that used it, now that CompoundImageAsset provides the same grouping in a much simpler way.
bumped the body text font size up slightly