Tree.Openable: Add missing API doc params.

Fixes #869
Build tree-openable. Doc changes only.
Merge branch 'live-docs' into dev-master
[#656] fix failing loader test on android 2.3.4

Removed an unnecessary if-else fork when checking to see wheter the `async`
configuration propagated to the DOM as expected.

Results of the investigation that support this change:
https://gist.github.com/ekashida/5762890