libpng source code
update binding.gyp to compile libpng
opens (decodes) png images

closes #19
clean libpng dir from unnecessary files
adds zlib dependency for windows

libpng needs zlib, which is not present by default on windows.
without it the compilation fails.
this commit adds zlib sources, and defines it as a dependency when
compiling under windows.

also updates copyright notices in the README.md file.
add waffle.io badge
Merge pull request #26 from waffle-iron/master

waffle.io Badge
integrate travis cli
adds travis badge
adds toPngBuffer
a bit of code organizing and cleanup
write (encodes) png buffers

0. adds JS land args validation
0. adds examples
0. updates readme

0. closes #20
adds tests to png encoding (#20)
Merge branch 'master' into png_support

Catch up with master
adds zlib dependency for all platforms
updates read me
Merge pull request #25 from EyalAr/png_support

PNG support