DataLayer to provide data from LIBSVM format file

I've just implemented a new layer which provides data from LIBSVM format file.

    <label> <index1>:<feature1> ... <index M>:<feature M>

Here is an example of using this layer: <http://nbviewer.ipython.org/github/tnarihi/caffe/blob/libsvmdatalayer/examples/libsvm_format_data_into_caffe.ipynb>