* Changes all agg_renderers to use a image_data_any variant (only image_data_rgba8 is implemented currently)
* Changes the marker and marker_cache to use image_data_any images
* Changes the symbolizers so that they must be aware of the source data type they are attempting to render and the render type that is expected to be rendered into.
* Moves many utilities into image_utils, that were previously in image_32.
The kicker is that this still isn't working perfectly yet, but I am commiting so I don't have tears in case everything is lost on my computer.
Ref #2633
The idea here is that much of the code in the renderers and the
various `process_*` rendering methods is shared, but this sharing
is obfuscated by the lack of sharing of renderer fields and
methods.
This is the first step in trying to factor out commonalities in
order to simplify the implementation of the renderers and make
them easier to understand and modify.
