Update code documentation comments to the newer style

[OrkhanAlikhanov]

This style comments:

 /**
  :name: removeValueForKey
  :description: Removes a single instance of a value for a key. This is
  important when using non-unique keys.
  - returns: Value?
 */
public func removeInstanceValueForKey(_ key: Key) -> Value? {}

Should be updated to the newer style:

 /**
  Removes a single instance of a value for a key. This is
  important when using non-unique keys.
  - Parameter _ key: A Key.
  - Returns: Removed Value for given key, nil on fail.
 */
public func removeInstanceValueForKey(_ key: Key) -> Value? {}

[daniel-jonathan]

This is a great issue to open. We can do it together.