* small cleanups in trie
* Memory trie skeleton
* decode nodes from RLP
* memorytrie -> memorytriedb
* implement Trie for MemoryTrie
* partially implement insert
* implement trie insertion
* don't load whole trie into memory, lookup across memory and db
* re-implement insertion and lazily load necessary nodes from DB
* node removal w/o fixing
* reduce churn in node storage
* finish remove implementation
* committing the in-memory trie
* reload root node after commit
* generate elastic arrays when converting nodes to rlp
* port triedbmut tests over to memorytriedb, fix a few bugs.
* hash count and dirty flag
* initial attempt for node inspection
* back to skeleton
* inspection framework
* implement insertion
* no panic paths in insert
* implement deletion without fixing
* node fixing
* commit nodes to db
* tracing targets and bugfix
* get tests to pass with a lot of tracing
* set playpen iterations to 10
* remove some tracing statements
* make TrieMut::root take &mut self
* replace triedbmut with memorytriedb
* treat empty insert value as removal
* add test for null insert
* fix some style concerns
* trie: use nodehandle for root_node, minor cleanup
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