Remove all default features. Making them opt-in

Cargo.toml

@@ -17,9 +17,12 @@ edition = "2021"
 rust-version = "1.60.0"
 
 [features]
-# TODO: Remove the default features on next breaking release and make them opt-in.
-# Because default features are evil
-default = ["std", "async"]
+# None of the features are on by default, by design. Default features is an anti-pattern.
+# Since most people pull in dependencies without carefully inspecting the dependency or
+# feature list, they accidentally pull in unnecessary complexity and sometimes even
+# dependencies. By making everything opt-in, we avoid this problem. Opting in to a feature
+# is so simple in Cargo anyway, and makes it more explicit what functionality it uses.
+default = []
 
 # Enables usage of libstd. Adds support for thread blocking receive methods.
 std = []