Implement JSON round-trip and fix specs

[ronaldtse]

Due to the "very unconventional" ways of ALI being used in JSON differing from how it works with XML, we needed to implement a Ali::Container class to contain the ALI JSON object.

The usages are rather strange as demonstrated below.

FreeToRead

FreeToRead can be an object or a Boolean.

spec/fixtures/json/spec_example_1.json

{
  "@context": "http://www.niso.org/schemas/ali/1.0.1/jsonld.json",
  "free_to_read": true
}

spec/fixtures/json/spec_example_1.json

{
"@context": "http://www.niso.org/schemas/ali/1.0.1/jsonld.json",
  "free_to_read": {
    "start_date": "2013-02-03",
    "end_date": "2013-10-03"
  }
}

LicenseRef

LicenseRef can be just a URI, one instance, or multiple instances:

spec/fixtures/json/spec_example_3.json

{
  "@context": "http://www.niso.org/schemas/ali/1.0.1/jsonld.json",
  "free_to_read": true,
  "license_ref": "http://creativecommons.org/licenses/by/3.0/"
}

spec/fixtures/json/spec_example_4.json

{
  "@context": "http://www.niso.org/schemas/ali/1.0.1/jsonld.json",
  "free_to_read": true,
  "license_ref": {
    "start_date": "2014-04-04",
    "uri": "http://creativecommons.org/licenses/by/3.0/"
  }
}

spec/fixtures/json/spec_example_6.json

{
  "@context": "http://www.niso.org/schemas/ali/1.0.1/jsonld.json",
  "free_to_read": true,
  "license_ref": [
    {
      "start_date": "2015-04-04",
      "applies_to": "https://doi.org/10.15223/asf-profile",
      "uri": "https://doi.org/10.15223/policy-005"
    },
    {
      "start_date": "2015-04-04",
      "applies_to": "https://doi.org/10.15223/asf-profile",
      "uri": "https://doi.org/10.15223/policy-025"
    },
  ]
}

TODO

• We need to provide proper JSON specs for FreeToRead and LicenseRef. (right now the JSON specs fail because all the examples are wrapped by a container)
• Handle the above mentioned cases of "unconventional" usages.