Vendor dependencies

Let's see how I like this workflow.

vendor/log/benches/value.rs

@@ -0,0 +1,30 @@
+#![cfg(feature = "kv_unstable")]
+#![feature(test)]
+
+extern crate log;
+extern crate test;
+
+use log::kv::Value;
+
+#[bench]
+fn u8_to_value(b: &mut test::Bencher) {
+    b.iter(|| Value::from(1u8))
+}
+
+#[bench]
+fn u8_to_value_debug(b: &mut test::Bencher) {
+    b.iter(|| Value::from_debug(&1u8))
+}
+
+#[bench]
+fn str_to_value_debug(b: &mut test::Bencher) {
+    b.iter(|| Value::from_debug(&"a string"))
+}
+
+#[bench]
+fn custom_to_value_debug(b: &mut test::Bencher) {
+    #[derive(Debug)]
+    struct A;
+
+    b.iter(|| Value::from_debug(&A))
+}