feat: implement support for bookmarks as well as internal hyperlinking

[Skelmis]

Example code:

from skelmis.docx import Document

doc = Document()
p = doc.add_paragraph()
p.add_internal_hyperlink("bookmark", "goto bookmark")
doc.add_page_break()

p = doc.add_paragraph()
p.add_bookmark(
    "bookmark",
    "hey look its bookmark display text",
)

doc.save("test.docx")

Tested:
add_bookmark:

• Libre
• OnlyOffice

add_internal_hyperlink:

• Libre
• OnlyOffice

Closes #20

Initial reference implementation taken from various comments on: https://stackoverflow.com/questions/57586400/how-to-create-bookmarks-in-a-word-document-then-create-internal-hyperlinks-to-t

[Skelmis]

PR is blocked until they work in Libre as well as we need that for PDF's...
Unsure why at a glance, it seems to be roughly correct syntax in the document.xml

[Skelmis]

Lib generated:

        <w:p>
            <w:hyperlink w:anchor="bookmark" w:tooltip="tooltip">
                <w:r>
                    <w:rPr/>
                    <w:t>goto bookmark</w:t>
                </w:r>
            </w:hyperlink>
        </w:p>

Libre generated:

        <w:p>
            <w:pPr>
                <w:pStyle w:val="Normal"/>
                <w:rPr></w:rPr>
            </w:pPr>
            <w:hyperlink w:anchor="bookmark">
                <w:r>
                    <w:rPr>
                        <w:rStyle w:val="Hyperlink"/>
                    </w:rPr>
                    <w:t>#bookmark</w:t>
                </w:r>
            </w:hyperlink>
        </w:p>

[Skelmis]

Wild, by not adding the tooltip Libre then recognises it as an internal hyperlink. If we set a tooltip then it fails to be recognised as a hyperlink