Support masks

[qrcodegen accepts `mask` parameter](https://github.com/nayuki/QR-Code-generator/blob/856ba8a74b48a6b3b32dd86f13b66b61b8579fcd/typescript-javascript/qrcodegen.ts#L90), and it'd be good if this library supports the parameter as well.

About QR code masks:
- https://en.wikipedia.org/wiki/QR_code#Encoding