feat(preload): $preload

+image
  id: "image1"
  url: "image1.png"

+audio
  id: "auido1"
  urls:
    - "audio1.ogg"
    - "audio1.m4a"

texture atlas
+atlas
  id: "atlas1"
  url: "atlas1.png"
  json: "atlas1.json"

+spritesheet
  id: "sprite1"
  url: "sprite1.png"
  frameWidth: 80
  frameHeight: 80
Merge branch 'master' into preload
chore: travis
chore: travis
chore: travis
chore: travis
chore: travis
docs: preload
docs: preload #16
Merge pull request #16 from kawax/preload

$preloadコマンド