Implement `From<&str> for ReactionType`
Implement `From<&str> for ReactionType`

Implement the ability to create a ReactionType from a string slice.

This is to be able to produce code like:

```rust
msg.react("🍎");
```

rather than needing to go the longer route:

```rust
msg.react("🍎".to_owned());
```

Lakelezz/serenity,zeyla/serenity,zeyla/serenity.rs,Roughsketch/serenity,acdenisSK/serenity,Flat/serenity,eLunate/serenity