test: paragraph_with_url

[yutatokoi]

Testing for different types of links in Markdown.

[yutatokoi]

My commits were conflicting with:

fn code_block() {
        let input = "<pre><code class=\"language-rust\">let x: i32 = 123;</code></pre>".to_string();
        let expected = "```rust\nlet x: i32 = 123;```\n".to_string();
        assert_eq!(from_html_to_md(input), expected);
}

which I removed in order to prioritise the other commits that I had made under this PR.