feat(env_filter): implement Clone for Filter

One of possible use-cases for Filter would be using it as a CLI argument,
so the user can configure the logger without setting any environment
variables. Right now it isn't possible to use Filter as a CLI argument
in clap, because clap requires all CLI arguments to implement Clone.

Author: InnocentusLime

crates/env_filter/src/directive.rs

@@ -1,7 +1,7 @@
 use log::Level;
 use log::LevelFilter;
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub(crate) struct Directive {
     pub(crate) name: Option<String>,
     pub(crate) level: LevelFilter,

crates/env_filter/src/filter.rs

@@ -192,6 +192,7 @@ impl fmt::Debug for Builder {
 /// Use the [`Builder`] type to parse and construct a `Filter`.
 ///
 /// [`Builder`]: struct.Builder.html
+#[derive(Clone)]
 pub struct Filter {
     directives: Vec<Directive>,
     filter: Option<FilterOp>,

crates/env_filter/src/op.rs

@@ -1,6 +1,6 @@
 use std::fmt;
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub(crate) struct FilterOp {
     #[cfg(feature = "regex")]
     inner: regex::Regex,