Intra-document links not created correctly

[mikechristiansenvae]

Given this markdown:

- [`cryptography` functions](#cryptography-functions)

LinkInlineRenderer.Write receives a LinkInline object, with a Url property of "#cryptography-functions".

Line 30 calls Uri.IsWellFormedUriString and since that returns false, the URI that is written is #.

[Kryptos-FR]

Indeed, internal anchors are not supported. Pull-request welcome.

It might be a bit tricky as it would need some post-processing to go through the whole object graph at the end of the "rendering" and also implement a custom command that would scroll into view for the corresponding anchor.

[isaksavo]

It seems there are two parts to this:

1. Using Uri.IsWellFormedUriString which returns false for things like #my-anchor. This can be solved by simply not calling this - just call Uri.TryCreate(url, UriKind.AbsoluteOrRelative) and it'll return true for #my-anchor, but false if you pass it null or something else that cannot be interpreted as a URI.
2. Make MarkdownViewer navigate to this intra-document links by scrolling to the correct location.

For people not using the built in viewer (for example me), there's value in fixing only 1 which should be trivial.

(I have my own derived LinkInlineRenderer for other reasons so I was able to work around this issue. Just bringing it up as a possible low hanging fruit for the next release)