Merge pull request #603 from akhenakh/64bits_support

64bits support (fix #572, fix #504, fix #494)
explicit webp detection
fixed code format
reformat code
upgrade libwebp to 0.4.0
Merge pull request #604 from akhenakh/webp_detect

Webp detect
Merge pull request #605 from akhenakh/upgrade_webp

upgrade libwebp to 0.4.0
use a NSInteger as size (cause we are using -1 as start indicator)