Make types implement Debug

[juh9870]

Currently, public structs from this crate don't implement Debug trait, which causes issues if I want to pass some toasts' creation options around (Commands pattern, for example), as well as goes against a pretty strong suggestion in Rust docs

[urholaukkarinen]

Currently most public structs do implement Debug, but some, like Toast and Toasts, have fields that themselves do not implement it, so those would need an explicit Debug impl. However, there's no reason why something like ToastOptions should not have Debug.