Support numeric and alphanumeric encodings

[paulhoule]

QR codes support compact encodings for codes that contain only digits or that contain only uppercase letters, digits and selected symbols.

Many QR code libraries automatically use the most efficient encoding possible. I took a look at the underlying qr.js library and found that it doesn't support encodings other than 8-bit but there are some others such as qrcode.js that do.

We could make smaller QR codes that are easier to scan if the underlying library was replaced with something that knows about alternate character sets.