Deal with XMLDOC references to mscorlib

[zsr2531]

An extremely common scenario when it comes to the <inheritdoc /> tag is when the user would like to inherit documentation from mscorlib (ie. Equals, ToString, GetHashCode, etc.). Since this is very common, an extra XMLDOC path shouldn't need to be provided by the user and Doktr should implicitly include it. This raises a couple of issues however:

• Where to store the XML file? As a resource? Just a normal file that you should "carry" around with Doktr?
• The XML file is pretty big. I haven't done any testing as of yet but I imagine that it will take a considerable amount of time to fully parse even when most of it probably won't be needed. This has the potential to slow Doktr down considerably.