Links that have `styleAttributes` don't add the URL attribute

[diogot]

As this snippet shows if there is a styleAttributes for links the url attribute is ignored.

MarkdownAttributedString/NSAttributedString+Markdown.m

Lines 474 to 479 in 750e8d5

	if (styleAttributes[MarkdownStyleLink]) {
	replacementAttributes = styleAttributes[MarkdownStyleLink];
	}
	else {
	replacementAttributes = @{ NSLinkAttributeName: URL };
	}

I need to customise the link color and keep them tappable.
I'll send a PR soon.