2.1
[Feature] Support Linux
[Performance] Update to apngasm 2.9.1
[Performance] Update to apngopt 1.4 (Linux 1.2)
[Performance] Update to pngout 20150319
[Performance] Update to pngquant 2.10.0 (Linux 2.5.0)
[Fix] Fix a bug that always show the tips the first time you launch if the current folder is empty