Strip out  tags before processing markdown

Strip out ![svekyll-img].. tags.

For example, you might have a blog post like this:

---
title: "comparing Claude Code and Aider"
published: true
date: 2025-02-28

attachments:
  organized_initiative:
    filename: myblog/2025-02-28_9924325_0.png
---

Aider is great. Claude might be even better. But, its still a race.

<svekyll-img src={attachments.organized_initiative.filename}>
![svekyll-img](https://imagehosting.com/myblog/2025-02-28_9924325_0.png)

Here is a longer discussion...

Why two image tags? Inside a gitlab or github editor, the svekyll-img tag will be ignored, but the other image tag will be rendered. If you want to use both a dynamically generated image URL that uses a base URL inside your _config.yaml then you can do this.

You can use regular ![My Alt Text](foo.png) image references and they will be preserved. And, this can be disabled using the config file (see the README for specifics).

First merge request with Claude Code. Here we go...