0.2.0 release
Merge branch 'master' of https://github.com/johnmccutchan/asset_pack

Conflicts:
	pubspec.yaml
Remove dependencies until pub is fixed.
operator[] no longer throws.

It returns null now and matches the behavior of Map operator[].

Signed-off-by: John McCutchan <john@johnmccutchan.com>
Merge branch 'master' of https://github.com/johnmccutchan/asset_pack
SDK fixes

Signed-off-by: John McCutchan <john@johnmccutchan.com>