(BREAKING) save_checkpoint(): Save dict of user values instead of best_top1

[guyjacob]

'best_top1' is too specific to classification workloads. Suggesting to just pass a dictionary of values instead, which will allow to pass anything the user deems worthy.
Also modified load_checkpoint to print a summary of the checkpoint contents, it looks something like this:

=> loading checkpoint logs/2019.04.04-131231/checkpoint.pth.tar
=> Checkpoint contents:
+----------------------+----------------+
| Key                  | Type / Value   |
|----------------------+----------------|
| arch                 | resnet20_cifar |
| best_epoch           | 1              |
| best_top1            | 58.06          |
| compression_sched    | dict           |
| current_top1         | 53.18          |
| epoch                | 2              |
| optimizer_state_dict | dict           |
| optimizer_type       | SGD            |
| state_dict           | OrderedDict    |
+----------------------+----------------+

For "simple" values it'll print the actual value, otherwise it prints the type.

[guyjacob]

@barrh please take a look, can't add you as a reviewer for some reason

[barrh]

I'd love to see if you could also return the extra values from load_checkpoint.
The request for changes is for the inline comment.