utils: add decodeNameCycle
ifaces: add Directory, ROOTUnmarshaler and ROOTMarshaler interfaces
ifaces: doc cosmetics
decoder: factorize decoding ROOT binaries
key: Key.Data -> Key.load
key: leverage ROOTUnmarshaler, introduce Key.Value
tree: introduce Tree data structure. rather limited at this point
file: doc cosmetics
file: cosmetics
file: add impl. of Directory interface
file: make sure File satisfies Directory interface
all: add tests for File as a Directory
test: limited test of a rootio.Tree