Make femme dependency optional

It now is only installed via the `logger` feature. In order to do this
we need the `std` feature from `log` crate.

Author: rossmacarthur

Cargo.toml

@@ -26,7 +26,7 @@ rustdoc-args = ["--cfg", "feature=\"docs\""]
 [features]
 default = ["h1-server", "logger", "sessions"]
 h1-server = ["async-h1"]
-logger = []
+logger = ["femme"]
 docs = ["unstable"]
 sessions = ["async-session"]
 unstable = []
@@ -39,9 +39,10 @@ async-session  = { version = "2.0.0", optional = true }
 async-sse = "4.0.0"
 async-std = { version = "1.6.0", features = ["unstable"] }
 async-trait = "0.1.36"
-femme = "2.0.1"
+femme = { version = "2.0.1", optional = true }
 futures-util = "0.3.5"
 http-types = "2.4.0"
+log = { version = "0.4.8", features = ["std"] }
 kv-log-macro = "1.0.4"
 pin-project-lite = "0.1.7"
 route-recognizer = "0.2.0"

src/log/mod.rs

@@ -21,7 +21,9 @@ pub use kv_log_macro::{max_level, Level};
 
 mod middleware;
 
+#[cfg(feature = "logger")]
 pub use femme::LevelFilter;
+
 pub use middleware::LogMiddleware;
 
 /// Start logging.