Vendor dependencies

Let's see how I like this workflow.

vendor/smallvec/scripts/run_miri.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/bash
+
+set -ex
+
+# Clean out our target dir, which may have artifacts compiled by a version of
+# rust different from the one we're about to download.
+cargo clean
+
+# Install and run the latest version of nightly where miri built successfully.
+# Taken from: https://github.com/rust-lang/miri#running-miri-on-ci
+
+MIRI_NIGHTLY=nightly-$(curl -s https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/miri)
+echo "Installing latest nightly with Miri: $MIRI_NIGHTLY"
+rustup override unset
+rustup default "$MIRI_NIGHTLY"
+
+rustup component add miri
+cargo miri setup
+
+cargo miri test --verbose
+cargo miri test --verbose --features union
+cargo miri test --verbose --all-features
+
+rustup override set nightly