Make ocfl-object specification version aware

[zimeon]

The current version of ocfl/object.py is hard-coded to version 1.0, e.g.:

ocfl-py> ./ocfl-object.py --show --objdir fixtures/1.1/good-objects/spec-ex-full
WARNING:ocfl.object:OCFL v1.1 Object at fixtures/1.1/good-objects/spec-ex-full has VALID STRUCTURE (DIGESTS NOT CHECKED)
WARNING:ocfl.object:Object tree
[fixtures/1.1/good-objects/spec-ex-full]
├── 0=ocfl_object_1.1 <--- ???
├── inventory.json 
├── inventory.json.sha512 
├── v1 
│   ├── content (3 files)
│   ├── inventory.json 
│   └── inventory.json.sha512 
├── v2 
│   ├── content (1 files)
│   ├── inventory.json 
│   └── inventory.json.sha512 
└── v3 
    ├── inventory.json 
    └── inventory.json.sha512 

The ??? is because the code is looking for a v1.0 declaration even though the validator is aware that it is a v1.1 object.