* Changed the passing of rgba_palette to a shared_ptr in order to better facilitate the use of a visitor pattern.
* Moved PNG util processing into its own set of files so that image_util_impl.hpp would not have to depend on HAVE_PNG.
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?
Example:
>>> from mapnik import *
>>> im = Image(200,200)
>> save_to_file('test.png',im) # Guess image type from file extension
>> save_to_file('test.png,'jpeg',im) # Explicitly save as JPEG
bool hit_test(double x, double y, double tol);
2. added image_view(unsigned x, unsigned y, unsigned width, unsigned height)
allowing to select region from image data e.g (in Python):
im = Image(2048,2048)
view = im.view(0,0,256,256)
save_to_file(filename,type, view)
3. changed envelope method to return vy value in datasource classes
4. features_at_point impl for shape and postgis plug-ins
