More descriptive naming schema for Precomputed

[MaxDall]

Currently the Precomputed class consists of very overloaded names while itself yielding not much information about it's nature through the class name:

class Precomputed:
    html: str
    doc: lxml.html.HtmlElement
    meta: Dict[str, str]
    ld: LinkedData
    cache: Dict[str, Any] = field(default_factory=dict)

The goal of this issue is:

• Find a new name for class Precomputed as well as the precomputed attribute of BaseParser
• Find more precise names for ld, doc, meta

The above list also include renaming those instances and this issue should be closed with a PR