implement extend trait to allow bulk updates to Trie

[skewballfox]

I'm not sure if this falls outside of the normal usecase, but currently there doesn't seem to be a way to merge two tries, the way there is with maps via the extend trait.

I'm currently trying deserializing multiple toml files(containing snippets) to a single trie. Currently my options for updating an existing data structure are to store every key, value pair in separate files (which I've implemented) and add them one by one, or to store groups of key, value pairs in a single file and use extend to update the DS

I'm pretty new to rust but I would like to help out with this, if you could give me some idea of how and where to implement this, I would appreciate it