Preserve raw content in $text node

[parzhitsky]

xml2json configured to automatically parse data to values (numbers, booleans, etc., falling back to strings). This means:

• remove this configuration of xml2json and parse values manually (ideally, preserving xml2json's parsing logic);
• save raw unparsed strings in $text property;

[parzhitsky]

ideally, preserving xml2json's parsing logic

Possibly extremely wasteful, but we could create two intermediate JSONs – one with raw data, and one with parsed data, – and then combine the results (data from parsed JSON comes to $data, and data from raw JSON comes to $text). That way, the third-party parsing logic would be preserved; on the other hand though, it only worsens the problem of having an intermediate processing (#1).

[parzhitsky]

Blocked by #6