Include ocfl spec in the repo

[alvinsw]

When creating or opening an ocfl storage, the library must ensure that the ocfl spec text file is added there.
There are four options to explore:

1. Copy the ocfl spec text to this library git repo.
2. Add the ocfl git repo as a submodule and include the spec when publishing in npm
3. Copy the spec text from the official ocfl when doing npm install
4. Copy the spec text from the official ocfl in real time (internet required)