* 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
image_data_32 -> image_data_rgba8
image_data_8 -> image_data_gray8
image_data_16 -> image_data_gray16
image_data_float32 -> image_data_gray32f
NOTE: currently image_data_gray16::pixel_type = std::int16_t (signed 16 bit int) to match GDAL
should we support unsigned types?
