+ factory : variadic templates based implementation ( requires c++11)
+ image_reader : stream based reading interface (boost::iostreams)
+ register additional png and jpeg readers with following sigs :

  ```
  std::auto_ptr<mapnik::image_reader> reader(mapnik::get_image_reader(buffer,size));
  // buffer - char const*
  // size - size_t
  ```
+ initial type_from_bytes implementation (TODO: add more types)
+ python : mapnik.Image.fromstring(str) mapnik.Image.frombuffer(buf)
+ remove const& qualifier
+ no iostreams lib dependency version
WEBP image reader

+ add initial support
+ cleanup include directives
+ fixes and improved error handling
+ fix crop width/height calc
webp_reader : implement reading from file
type_from_filename : add webp support
+ update image_io test to support WEBP
+ image_reader : consistent error handling - throw image_reader_exception rather than returning 0 pointer.
Merge branch 'master' into image-readers-c++11
+ add getBytes() method ( needed by webp i/o)
+ add webp writing support
+ add webp support
+ output webp

quality=100 -> demo.webp
quality=80  -> demo-med.webp
qiality=50  -> demo-low.webp

TODO: support other webp writing options
Merge branch 'master' into image-readers-c++11

Conflicts:
	include/mapnik/factory.hpp
+ use nullptr
+ fix : output file_name
+ png_io: disble miniz for now