support for <see cref="" /> links in xml documentation.

This commit adds support for ```<see cref=""/>``` annotations (http://msdn.microsoft.com/en-us/library/cc837134.aspx).
NOTE: This only works when markup parsing is disabled (otherwise the markup parser is used). So you need to use the ```markDownComments = false``` parameter in the ```MetadataFormat.Generate``` method.
We first try to resolve the type within the project and then fall back and generate a msdn link (for example "http://msdn.microsoft.com/en-us/library/System.AppDomain").