Add Getters for Headers, Footers, Images, and Links

[ttrasn]

This pull request introduces new getter methods to the docx object, providing users with convenient access to the following parameters:

• Headers: Retrieve the headers from the document.
• Footers: Retrieve the footers from the document.
• Images: Retrieve the images embedded in the document.
• Links: Retrieve the hyperlinks present in the document.

These enhancements improve the functionality of the docx library by allowing users to easily access and manipulate document headers, footers, images, and links, which can be useful for various document processing tasks.