Change FluentArgs key type to String.

[XAMPPRocky]

Currently FluentArgs is a HashMap<&str, FluentValue>, which is okay when you're using str literals as keys, however when you're constructing your map dynamically you don't have a HashMap<&str, V> only a String. Currently you have to construct a new HashMap that takes the key by reference and clones the FluentValue. It would easier for users and more appropriate if it was HashMap<String, FluentValue>.

// Current
pub type FluentArgs<'args> = HashMap<&'args str, FluentValue<'args>>;
// Proposed
pub type FluentArgs<'args> = HashMap<String, FluentValue<'args>>;

[zbraniecki]

Hmm, I'm torn on this. I'm wondering if there's a way to handle both scenarios without having to give up on the former.

[zbraniecki]

See #94 for the motivation for current design.

[XAMPPRocky]

@zbraniecki AFAIK the best way to handle this would be Generic Associated Types but that isn't currently available. I don't know what the best workaround would be but with the current API I can actually be allocating more since I have to construct a new map with each key by reference and each value by value versus just allocating a string each time. If I wanted to reduce allocations with Fluent I could do that on the user side with memoization for the argument map but I actually can't use memoization on FluentArgs currently because memoization requires owning the data in some way.

[zbraniecki]

@XAMPPRocky can you check if the current master branch solved it? I switched FluentArgs to accept Cow which hopefully solves it.

[XAMPPRocky]

Yeah Cow works for me. Thanks for working on this!