Allow hints to be passed to encode_barcode

[cpwood]

Currently, a new, empty HashMap is passed into the Rust library when encode_barcode is called. However for Telepen Numeric, I would need to pass a hint.

Could there either be an additional method - e.g. encode_barcode_with_hints?

[hschimke]

good idea, I'll work on getting this implemented.

[hschimke]

fully untested and unstable, but an initial version appears in 4f84efa v0.2.2 on NPM now