Added support for ActionName attribute in XML comments

Added support to ApplyActionXMLComments for ActionName attribute.  Fixes
#118
I'm being a bit nitpicky but I don't think all the checks are necessary ... because XML comments will always use the declared name, then we should probably just always go with that (maybe fallback to ActionName as a last resort). For example:

    var reflected = actionDescriptor as ReflectedHttpActionDescriptor;
    var actionName = (reflected != null) ? reflected.MethodInfo.Name : actionDescriptor.ActionName