Import atomic package

The code is the same as github.com/uber/tchannel-go/atomic

scripts/cover.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+set -e
+
+COVER=cover
+ROOT_PKG=github.com/uber-go/atomic
+
+if [[ -d "$COVER" ]]; then
+	rm -rf "$COVER"
+fi
+mkdir -p "$COVER"
+
+i=0
+for pkg in "$@"; do
+	i=$((i + 1))
+
+	extracoverpkg=""
+	if [[ -f "$GOPATH/src/$pkg/.extra-coverpkg" ]]; then
+		extracoverpkg=$( \
+			sed -e "s|^|$pkg/|g" < "$GOPATH/src/$pkg/.extra-coverpkg" \
+			| tr '\n' ',')
+	fi
+
+	coverpkg=$(go list -json "$pkg" | jq -r '
+		.Deps
+		| map(select(startswith("'"$ROOT_PKG"'")))
+		| map(select(contains("/vendor/") | not))
+		| . + ["'"$pkg"'"]
+		| join(",")
+	')
+	if [[ -n "$extracoverpkg" ]]; then
+		coverpkg="$extracoverpkg$coverpkg"
+	fi
+
+	go test \
+		-coverprofile "$COVER/cover.${i}.out" -coverpkg "$coverpkg" \
+		-v "$pkg"
+done
+
+gocovmerge "$COVER"/*.out > cover.out