Case sensitivity and coercion

[stuartpb]

As previously discussed in opws/opws-dataset#23

[stuartpb]

USPS.com (opws/opws-dataset#321) notes that usernames are case-sensitive (which is especially weird, considering that they suggest using your email address as a username, and domains are case insensitive).

Also, worth noting, and continuing a point that was brought up in opws/opws-dataset#23: wellsfargo.com, of all places, treats passwords as case-insensitive. This came up in a discussion on Twitter a while back, I think I linked to the wellsfargo.com profile, but I didn't file an issue for it.

The old issue suggested that case-insensitive passwords be listed as "redflags", but that's an older concept from back before I considered all password use to be a red flag: at this point, it'd just use the same kind of datapoint as case-insensitive usernames.