updates Hash conversion methods to be applied using postponed amendme…

…nt, updates dependencies, version bump

updates dependencies

adds .save() to "not saved" warning

makes callback handler optional in Json.write()

updates dependencies and adds value argument to tree unset callbacks …

…where applicable

updates readme for 0.2.0 features

makes handlers optional in annotation

version bump

separates PersistedTree.read() method from constructor

changes KeyValueStore.read() to return root node to read handler