Implement RedundantXMLDocParameter

[Vannevelj]

This resembles #188 but works the other way around: show a warning and offer to remove an XML doc parameter comment if there is no corresponding parameter.

This:

/// <param name="a"> First param </param>
/// <param name="b"> Non-existing param </param>
public void MyMethod(int a) { }

becomes

/// <param name="a"> First param </param>
public void MyMethod(int a) { }