rewrite quite many trie codes, _update_kv_node not finished yet
finished: _update_kv_node. need testing
fix some bugs, still not complete
Merge branch 'master' of github.com:ethereum/pyethereum
Merge branch 'master' of github.com:ethereum/pyethereum
1. close #34: rewritten update/get code
2. need to check correctness using data from the `test` project
Merge branch 'master' of github.com:ethereum/pyethereum