Replace unmaintained unidecode with deunicode

[Vogeltak]

The unidecode crate appears to be unmaintained. For similar reasons as in #38, we can replace this dependency with the deunicode crate that explicitly positions itself as an alternative.

This currently breaks the emojis test in src/lib.rs. I couldn't quickly figure out how to best fix this. Thought that you might have some insights here?

[djudd]

Haven't had time to look at this yet - I'm afraid replacing unidecode doesn't seem super urgent to me since despite being unmaintained it also seems kinda "done" - but wanted to note that I did see this and will investigate more at some point. Appreciate the PR.