feat: expose wordlists as an enum

The enum optionally implements (de)serialization with serde, when that feature is enabled and has a function for getting a word list out of it. This is useful for cases like config files, where you'd want to store a preferred word-list or something like that.

While at it, I've also set the path in the diceware deps for the wordlists crate. For details on how this behaves, see https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#multiple-locations. tl;dr: Allows to modify both at the same time to make development easier, but pulls from the version published on crates.io when built from there. To ensure this doesn't break anything, the wordlists crate needs to be published before the diceware crate itself for the next time.