Rust SDK 2 SQLite `Value` helpers

[itowlson]

I'm updating the docs for the Rust SDK.

It seems like we used to support ValueParam::Text("something") but the new Value enum only accepts owned Strings e.g. Value::Text("something".to_owned()). Is it possible to make this more flexible, e.g. adding a From(&str) implementation? (or am I missing where we already have a friendly conversion method)