Support set picture fill max screen width, and support set call back when click picture

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From #108 #73 .

Add imgFillMaxWidth: Boolean to MarkdownParseOptions, which can make img fill parent's layout max width.

And add onImgClicked: ((String) -> Unit)? = null to RichTextScope.Markdown, which support call onImgClicked(url) when picture in MarkDown be clicked.

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This is set imgFillMaxWidth = true:

And this is false:

About click img:

              Markdown(
                content = sampleMarkdown,
                markdownParseOptions = markdownParseOptions,
                onLinkClicked = {
                  Toast.makeText(context, it, Toast.LENGTH_SHORT).show()
                },
                onImgClicked = {
                  Toast.makeText(context, it, Toast.LENGTH_SHORT).show()
                }
              )

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@halilozercan Hello, please check this PR, thanks

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#114 better than this