Vendor dependencies for 0.3.0 release

vendor/slotmap/build.rs

@@ -0,0 +1,17 @@
+fn main() {
+    let is_nightly = version_check::is_feature_flaggable() == Some(true);
+    let is_at_least_1_49 = version_check::is_min_version("1.49.0").unwrap_or(false);
+    let is_at_least_1_51 = version_check::is_min_version("1.51.0").unwrap_or(false);
+
+    if !is_at_least_1_49 {
+        println!("cargo:warning=slotmap requires rustc => 1.49.0");
+    }
+
+    if is_at_least_1_51 || is_nightly {
+        println!("cargo:rustc-cfg=has_min_const_generics");
+    }
+
+    if is_nightly {
+        println!("cargo:rustc-cfg=nightly");
+    }
+}