Add custom end marker for comment templates

[UnexomWid]

When writing other templates in a comment template, the template ends must be escaped. This can become annoying, as you have to un-escape all ends if you decide to uncomment the templates in the future.

[|//
    [| template here \|]
    [|@ it : array \|]
|]

It would be better if comment templates had a special end marker, like this:

[|//
    [| template here |]
    [|@ it : array |]
//|]

In this case, the marker is //|], so the templateEnd marker can be included in the comment without any issues.

Also, a proper option should be added for this marker.