After MSRV bump `try_from` usually refers to `TryFrom` method but
`CommandString` used inherent one making it confusing and non-idiomatic.
This implements `FromStr` and `TryFrom<{stringly type}>` for
`CommandString` and deprecates the inherent method in favor of those.
To keep the code using `&'static str` efficient it provides
`try_from_static` inherent method that only converts from
`&'static str`.
Closes#1135
405be52f5c