is-webp

I made extended version of this package, which added support of Animated WebP detection. Since WebP Container is based on RIFF, and requires seeking to read animation related bitstream. i thought adopting animation webp detection feature will break your simple code (that's the reason why i love your packages also haha), and it's hard to support "isomorphic package" (e.g. Node Stream, Browser blob...) i decided to make new my own version of instead of breaking your simple code. and i made it! ;) (also there is another related package for Node environment - node-webpinfo - check it out!)