Derive Default for Level and LevelFilter enums

[ssrlive]

When using log crate, we might sometimes define a struct with the Default macro,
but if Level or LevelFilter doesn't implement the Default trait, this struct will fail to compile.

Therefore, I created this PR. I hope you will approve it and merge it.

#[derive(Debug, Clone, Default)]
pub struct Args {
    pub item1: Option<String>,

    /// Log level (off, error, warn, info, debug, trace)
    pub log: log::LevelFilter,
}

[Thomasdezeeuw]

I'm not sure about implementing default for the level, I imagine we might not be able to agree on what the default should be.

Btw you can also implement Default manually, this way you can continue with your project without having to wait on this.

[KodrAus]

Thanks for the PR @ssrlive! I share the same reservations as @Thomasdezeeuw, and don’t believe we should implement Default for level. There are reasonable arguments for picking the lowest/highest/info and none is a universal default.