Improve whitespace in diagnostics popup

[braver]

Fixes #105

Currently, descriptive text just sits in the parent element and cannot be targeted with CSS without also affecting code snippets. This PR solves that by wrapping it in a div.text.

However, if there is a newline between divs it is rendered as a blank line. This shouldn’t happen in regular HTML or Markdown, but this isn’t regular. This causes two problems:

1. A disproportionate amount of white space between code snippets and text. This is solved by shifting text half a line upwards, making it sit nicely centered vertically.
2. Succeeding lines have a blank line between them. This isn’t terrible, but it wasn’t there before the PR, so I solved it by removing the \n before a div. Fenced Code blocks should be followed by a newline so that’s ensured when the block is added.

I had a little side-issue with any text after a \r\n not being rendered. I dunno why, also don’t know why there would be a \r\n, must be something to do with TypeScript being a Microsoft thing and giving us Windows line endings or something. It also caused double newlines to not be respected. I solved that by converting \r\n to \n.

Content in a div.text is now also rendered with a sans-serif font.

Before

After

PS. My fork seems a bit messy, I’ll clean that up in a second.