use ToValue as the bound for captured values

[KodrAus]

Hi! 👋

This PR allows any T: ToValue to be used as the value in a captured key-value pair instead of just strings. See: rust-lang/log#353 where we should also make this change.

Description

Instead of expecting a &[(&str, &str)], we can take a &[(&str, &dyn ToValue)], which still implements the Source trait. That way values like integers can also be captured, along with more complex values if they use an adapter.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[yoshuawuyts]

Ohhhhhh, this is fantastic. Thanks so much for sharing!!