link hash SHA256 base64 encoding, and length integer

[danielweck]

https://readium.org/lcp-specs/releases/lcp/latest.html#35-pointing-to-external-resources-the-links-object

length - Content length in octets - Integer

hash - SHA-256 hash of the resource - Base 64 encoded octet sequence

"example 3":

    { "rel": "publication",
      "href": "https://www.example.com/file.epub",
      "type": "application/epub+zip",
      "length": "264929",
      "hash": "8b752f93e5e73a3efff1c706c1c2e267dffc6ec01c382cbe2a6ca9bd57cc8378"
    },

...as you can see, the example shows hash as a hex-encoded value, not b64. Furthermore, length is a string, not an integer.

The Go implementation produces hash as hex-encoding, and length as number value:

• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/index/index.go#L33
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/license/license.go#L62
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/license/license.go#L258C14-L258C19
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/license/license.go#L281
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/index/index.go#L34
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/license/license.go#L63-L64
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/license/license.go#L259C14-L259C23
• https://github.com/readium/readium-lcp-server/blob/f56eaae46535cf3729e0d60a2f474e98dcf6effe/license/license.go#L282

See examples of LCP license JSONs generated by the Go implementation:

https://www.edrlab.org/readium-lcp/testing-readium-lcp-compliant-devices/

Suggested fix:

1. replace "base64" with "hex encoding"
2. fix the length example by replacing the string with an integer