Add in-tree buildkite pipeline

ci/coverage.sh

@@ -0,0 +1,17 @@
+#!/bin/bash -e
+
+cd $(dirname $0)/..
+
+source $HOME/.cargo/env
+rustup update
+export RUST_BACKTRACE=1
+cargo build
+cargo kcov
+
+if [[ -z "$CODECOV_TOKEN" ]]; then
+  echo CODECOV_TOKEN undefined
+  exit 1
+fi
+
+bash <(curl -s https://codecov.io/bash)
+exit 0