? add output transformations
+ support for non-8bit data
+ stream exceptions: badbit only
+ adjust png::image for non-memory back end buffer + row-by-row io
+ use doxygen
- add optional and unknown chunks handling
+ change bit_depth to size_t
+ move tests sources to test/, examples to examples/
+ extract common code from generator/consumer
+ update pixel traits to detect channels count
+ unify template parameters naming
+ make sure all headers compile on their own
+ add compilation dependency detection
+ add pixel_buffer/image::operator[]
+ improve docs and README
? endianness in expand_8_to_16()
- unify error messages (capitalization, etc.)
+ move stream template parameter from class to function level in
  generator and consumer
+ make all tests run even if any of them fails
