Add empty string equality to null test
disable the hsla image-filter - not yet ready for primetime
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