Compatibility issues with MarkdownSharp

[Matt Richardson]

There are a few other compatibility issues, but not as impacting as #75 .

1. Transform in the MarkdownSharp code base returns the string with a trailing \n, whereas this one does not.
2. AllowEmptyLinkText defaults to false whereas I think it needs to default to true to keep matching behaviour.

[red]

1). I cant find nothing about this in md spec. There are good reasons to add it ?
2). It makes sense (but I do not like that you can create a hidden link). Create PR or I'll do it but later.

[Matt Richardson]

I'm more thinking more from a in-place replacement point of view rather than whether its a good idea or not :)

If i get a chance I'll create the PR, but as there's a workaround its not as high on the priority list.

[red]

@matt-richardson AllowEmptyLinkText currently = true
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