Split code up into three libraries to fix #37:
- asset_pack_common: All base code
- asset_pack_browser: Depends on dart:html, contains a AssetManagerBrowser that registers all browser related loaders
- asset_pack_standalone: Depends on dart:io, contains a AssetManagerStandalone that registers all standlone VM related loaders (unifished)
Merge branch 'master' into feature/server-support
#37 Add basis standalone VM text loader and refractor some code
Merge pull request #40 from Fox32/feature/server-support

Make it possible to use asset_pack without dart:html