Merge pull request #25 from hakobera/feature/update-dependencies

Update dependencies

Merge pull request #22 from hakobera/feature/use-external-decoder

Decoder を外部パッケージに移動。合わせて go 1.14 以上を必須にした

Merge pull request #21 from hakobera/example/sdl2-support-vp9

example/sdl2 VP9のサポート

Merge pull request #20 from hakobera/update-readme

README を更新

Merge pull request #2 from hakobera/feature/datachannel

DataChannel をサポート