Weak default parameters

Via [this thread](http://www.openwall.com/lists/crypt-dev/2012/09/02/1), direct quote from Colin Percival:

```
> Overall, I think scrypt at 1 MiB is not a good replacement for bcrypt
> currently.  We need bigger settings.

I agree.
```

Suggested memory usage for [100ms is 16MB](http://www.openwall.com/lists/crypt-dev/2012/09/10/4) - perhaps a more reasonable default than 200ms/1MB?
