Specialized core Locator extensions for "HTML": CSS Selector, Partial CFI and DOM Range

[danielweck]

Follow-up from: #98 and #95

TODO: agree on naming, define the JSON Schema
For example:

{
    "href": "http://example.com/chapter1",
    "type": "text/html",
    "title": "Chapter 1",
    "locations": {
        "progression": 0.8,
        "fragments": [
            "#paragraph-id",
            "t=15"
        ],
        "cssSelector": "body.rootClass div:nth-child(2) p#paragraph-id",
        "partialCfi": "/4/2/8/6[paragraph-id]",
        "domRange": {
            "start": {
                "cssSelector": "body.rootClass div:nth-child(2) p#paragraph-id",
                "textNodeIndex": 0,
                "offset": 11
            },
            "end": {
                "cssSelector": "body.rootClass div:nth-child(2) p#paragraph-id",
                "textNodeIndex": 0,
                "offset": 22
            }
        }
    }
}

[danielweck]

Let's continue to discuss the specifics of domRange here:
#95

[danielweck]

First draft:
https://github.com/readium/architecture/blob/master/locators/extensions/html.md

[llemeurfr]

Specification moved to: https://github.com/readium/architecture/blob/master/models/locators/extensions/html.md