Add option to add floating images on titlepage

[timonbldw]

Multiple Floating Logos for Title Pages

Feature Description

This PR enhances the title page customization by introducing support for multiple floating logos with positioning and sizing controls.

New Functionality

Users can now:

• Add multiple logos to the title page
• Control each logo's position using anchor points
• Adjust logo positions with $x$ and $y$ shifts with simplified positioning relative to the anchor points and towards the page center
• Define custom sizes for each logo

Example Configuration

---
title: "The Document Title"
author: [Example Author, Another Author]
date: "2017-02-20"
keywords: [Markdown, Example]
titlepage:
  text-color: "FFFFFF"
  rule-height: 0
  background: "background.pdf"
  logo:
    - path: "first-logo.pdf"
      anchor: "north east"
      xshift: 15mm
      yshift: 15mm
      width: 65mm
    - path: "second-logo.pdf"
      anchor: "south east"
...

Here is the actual document text...

Preview with 10 images:

Backwards Compatibility

• Maintains full compatibility with existing configurations
• Legacy parameters (e.g., titlepage-text-color) continue to function as before
• The original titlepage-logo parameter remains fully supported and unchanged

Documentation

• README has been updated to reflect new functionality
• Added examples and usage guidelines for the new logo positioning system

Testing

• Tested with various logo combinations
• Verified backwards compatibility with current examples

Please review and provide feedback on the implementation and documentation.

[Wandmalfarbe]

Thank you for this nice contribution! I currently don't have much time to work on this project, so PR review might take some time.