Vendor dependencies

Let's see how I like this workflow.

vendor/flate2/tests/zero-write.rs

@@ -0,0 +1,8 @@
+extern crate flate2;
+
+#[test]
+fn zero_write_is_error() {
+    let mut buf = [0u8];
+    let writer = flate2::write::DeflateEncoder::new(&mut buf[..], flate2::Compression::default());
+    assert!(writer.finish().is_err());
+}