Progress Monitoring

There should be a way to monitor progress. For example

### one option would be to add a parameter to print useful metrics to the screen
a parameter could be added to the initialization of the dk iterator, or to the synthesize method, which would cause progress to be printed on the screen

### another option would be to add interface to allow the user to control progress through the iterations
For example:

```
for i in dk_iter.synthesize(...):
print(i.peak_mu)
```

I tried using dk_iter.synthesize as an iterable as above, but I'm not sure how it works. In one place the docs say that an `IterResult` object is returned from `synthesize`, but the main example shows the results as a tuple `K, N, mu, d_scale_fit_info, info`. edit: ok i see the `IterResult` is inside the tuple. so in anycase you can't actually use it as in the above example to provide progress updates because it is not available until the synthesis is complete.