Rename fmt to parse

[hellow554]

I was very confused in the first place, that afmt::fmt actually is meant for parsing. When I first saw fmt I thought it would implement std::fmt::Display and I thought, hey! That's neat!

But only after looking at the sources (and reading the doc 🙃) I saw it's actually meant for parsing a string into a struct.

Maybe consider renaming the struct?
Next step would be to have a fmt macro that implements std::fmt::Display? Because that would be sick as well!

[eduardvercaemer]

I can see fmt being a little confusing, my thinking was that we are giving a 'format' to a data structure, I'll consider renaming it to parse.

I can also see the option of implementing both std::fmt::Display and std::str::FromStr.

Thanks for the feedback !