Render uses mipmaps
JSON spec and Beanshell generator updated accordingly
Mipmaps are required to be generated by area averaging all pixels with
the same floor(x*scale) coordinate with scale = 1/2^mipmap_level
using --scale <double> or --mipmap_level <int> enables generating
downscaled images, --area_offset simulates the corresponding mipmap
level shift as if the averaging scale method had been used to generate
the scaled image.  --quality <float> specifies the compression quality
if JPEG is used for saving.