title: equivalent of tf.dense in chainer
body: <p>As the documentation of tf.dense states for this layer the output tensor is the same shape as inputs except the last dimension is of size units. I was trying to have similar behavior in Chainer but I was not successful.</p>
  
  <p>In Tensorflow one can have a (32, 28, 28, 512) tensor and feed it as input to a linear layer and get a (32, 28, 28, 256). As I <a href="https://stackoverflow.com/questions/52089601/keras-dense-layers-input-is-not-flattened/52092176#52092176">researched</a> about the tf.dense, seems like when the input has more than 2 dimensions, it shares the weights and it doesn't flatten the input before performing the function. </p>
  
  <p>The chainer.links.Linear does flatten the input and as a result, it does not fit in the memory. I was wondering if it's possible to have the same functionality as in tf.dense somehow in Chainer?</p>