2.0

[Feature] Support APNG to Animted WebP converter
[Feature] Support i18n for English, Simplified Chinese and Traditional Chinese
[Performance] Update to nw.js 0.12.3
[Performance] Update to libwebp 0.6.0
[Performance] Update to apngopt 1.4
[Fix] Fix bug that apng convertor not check only 1 image and some tips issues
[Fix] Fix bug that imglossless convertor does not check JPEG and GIF images