title: Can't add keyValuePair directly to Dictionary
body: <p>I wanted to add a <code>KeyValuePair&lt;T,U&gt;</code> to a <code>Dictionary&lt;T, U&gt;</code> and I couldn't. I have to pass the key and the value separately, which must mean the Add method has to create a new KeyValuePair object to insert, which can't be very efficient. I can't believe there isn't an <code>Add(KeyValuePair&lt;T, U&gt;)</code> overload on the Add method. Can anyone suggest a possible reason for this apparent oversight?</p>