Ignore comments that don't start with TOC

[movermeyer]

I wanted to add an attribution to my TOC, so people knew that I used Markdown TOC to generate it.

<!-- Generated with "Markdown TOC" extension for Visual Studio Code -->
<!-- TOC -->
- [Version 2.0.1](#version-201)
- [Version 2.0.0](#version-200)
    - [Breaking changes](#breaking-changes)

<!-- /TOC -->

But this didn't work, since Markdown TOC looks for any comment that has TOC anywhere in the comment. It stripped the comment entirely.

Surpisingly, it doesn't even have to be upper case, nor a separate word:

<!-- This is the README for the stockfish project -->
<!-- TOC -->
- [Version 2.0.1](#version-201)
- [Version 2.0.0](#version-200)
    - [Breaking changes](#breaking-changes)
<!-- /TOC -->

It still stripped the comment entirely, despite TOC only appearing in "stockfish"

I would like for Markdown TOC to:

1. Ignore comments that don't start with TOC
   • Perhaps match the regex <!--\s*TOC
   • Perhaps match case sensitive (unless there is a reason not to)

[movermeyer]

As a short-term workaround, you can insert zero-width spaces (U+200B) characters between the TOC characters in your comments.

That way, the current regex doesn't notice the line.