Schema must be de/serialized from a json format

[qdequele]

Thanks to a previous issue #47 Schema can be built from a toml file.

The proposal for this issue is to handle the JSON format like the Toml format.

An example of the json schema:

{
    "identifier": "id",
    "attributes": {
        "id": {
            "strored": true
        },
        "title": {
            "strored": true,
            "indexed": true
        },
        "description": {
            "strored": true,
            "indexed": true
        },
        "image": {
            "indexed": true
        }
    }
}