Feature: allow generic attribute prefixes, e.g. data-*

[mcleanmds]

In the current implementation (v0.2.9), there isn't a way to allow all data-* attributes (or other generic attributes prefixes)

In the underlying ammonia, the builder allows for generic_attribute_prefixes to be specified, and uses the data- prefix as an example in the docs:
https://docs.rs/ammonia/latest/ammonia/struct.Builder.html#method.generic_attribute_prefixes

I am currently using bleach with an implementation that allows all data-* attributes, and I would like to switch to this library.
Having this ability would allow me to make the switch easily.

Please consider adding this feature.