Add buildpack.toml and publish script (#548)

Add buildpack.toml and publish script

buildpack.toml

+[buildpack]
+name = "Node.js"
+
+  [publish.Ignore]
+  files = [
+      "etc/",
+      "test/",
+      ".github/",
+      ".travis.yml",
+      "makefile"
+  ]
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etc/publish.sh

+#!/bin/bash
+
+set -e
+
+BP_NAME=${1:-"heroku/nodejs"}
+
+curVersion=$(heroku buildpacks:versions "$BP_NAME" | awk 'FNR == 3 { print $1 }')
+newVersion="v$((curVersion + 1))"
+
+read -p "Deploy as version: $newVersion [y/n]? " choice
+case "$choice" in
+  y|Y ) echo "";;
+  n|N ) exit 0;;
+  * ) exit 1;;
+esac
+
+originMaster=$(git rev-parse origin/master)
+echo "Tagging commit $originMaster with $newVersion... "
+git tag "$newVersion" "${originMaster:?}"
+git push origin refs/tags/$newVersion
+
+heroku buildpacks:publish "$BP_NAME" "$newVersion"
+
+echo "Done."
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