Add deprecation lints if using impl-* feature gates.

Cargo.toml

@@ -13,12 +13,6 @@ readme = "README.md"
 
 edition = "2021"
 
-[badges]
-travis-ci = { repository = "phaazon/splines", branch = "master" }
-is-it-maintained-issue-resolution = { repository = "phaazon/splines" }
-is-it-maintained-open-issues = { repository = "phaazon/splines" }
-maintenance = { status = "actively-developed" }
-
 [features]
 default = ["std"]
 impl-cgmath = ["cgmath"]
@@ -38,7 +32,7 @@ float-cmp = ">=0.6, < 0.10"
 serde_json = "1"
 
 [package.metadata.docs.rs]
-all-features = true
+features = ["std", "cgmath", "glam", "nalgebra", "serde"]
 
 [[example]]
 name = "hello-world"

src/lib.rs

@@ -108,6 +108,17 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(not(feature = "std"), feature(alloc))]
 #![cfg_attr(not(feature = "std"), feature(core_intrinsics))]
+#![cfg_attr(
+  any(
+    feature = "impl-cgmath",
+    feature = "impl-glam",
+    feature = "impl-nalgebra"
+  ),
+  deprecated(
+    since = "4.2.0",
+    note = "you are using an impl-* feature gate; please switch to * (e.g. impl-cgmath becomes cgmath)"
+  )
+)]
 
 #[cfg(not(feature = "std"))]
 extern crate alloc;