* Initial implementation, some redundancy is awkward and there is
some useless computation (but there is a pending pr for that).
Next are tests.
* Minimal tests and fix extend child.
* implement iterator for change child trie.
* prune child trie.
* Fix pruning test.
* bump spec version.
* Avoid empty child trie (could also be checked before)
* tabs.
* Fix child digest overriding each others.
* Restore doc deleted on merge.
* Check correct child value on extrinsics build.
* Revert runtime version update.
cheme
e3d0c60a31