Add Support for Parsing Lists

[mridul262]

What does this change?

Made the numbering structs public, to be able to parse lists in docx files using the docx-rs api, without generating to json.

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[mridul262]

@bokuweb thanks for this library! I've been using this library to parse word documents in rust and while trying to parse lists I noticed that these structs were set to private, so the only way to parse lists and determine whether they are bullets or numbered lists, as well as the type of list is to parse the json. Since it'd be much easier and efficient to parse directly in Rust, have opened the PR