This creates a generalized trait called TrieMut with the three basic Trie operations
that supports GC. Based on that, we have Secure/Any/Fixed TrieMuts.
- Rename: singletonmemorytriemut -> memorytrie
- Rename MemoryTrieMut and add TrieMut traits
- Add memory triemuts type declarations
- Implement the trieMut interface
- Fix tests due to interface change
- Update block to use trie 0.4