* In progress, runtime io must switch to future proof root +
child_specific (unique id) + u32 type.
* Switch interface, sr-io seems ok, rpc could use similar interface to
sr-io, genesis json broken if there is child trie in existing encoding
genesis.
* test from previous implementation.
* fix proving test.
* Restore Keyspacedb from other branch, only apply to child trie.
* Removing unneeded child_info from child root (child info are stored
if things changed, otherwhise the root does not change).
* Switch rpc to use same format as ext: more future proof.
* use root from child info for trie backend essence.
* Breaking long lines.
* Update doc and clean pr a bit.
* fix error type
* Restore removed doc on merge and update sr-io doc.
* Switch child storage api to use directly unique id, if managed id
where to be put in place, the api will change at this time.
* Clean deprecated host interface from child.
* Removing assertion on child info (can fail depending on root
memoization).
* merging child info in the overlay when possible.
* child iteration by prefix using child_info.
* Using ChainInfo in frame support. ChainInfo gets redesign to avoid
buffers allocation on every calls.
* Add length of root to the data of child info.
* comments
* Encode compact.
* Remove child info with root.
* Fix try_update condition.
* Comment Ext child root caching.
* Replace tuples by struct with field
* remove StorageTuple alias.
* Fix doc tests, and remove StorageOverlay and ChildStorageOverlay
aliases.
Shawn Tabrizi