More functions for saving/loading parameter

[hantek]

If the deep network is stacked by layers of autoencoders, then the current save_params() and load_params() does not save the parameters in the decoders.

And, it doesn't provide a more flexible way of saving/loading, eg., specify which parameter to load on to which layer, or load part of the parameters from the file.

We need more powerful solutions and deprecate the former pair of functions.