Add `release` script

The script handles bumping up the version number, committing, tagging
and updating the Homebrew formula. The last step requires `hub` to be
installed in order to submit a pull request to Homebrew.

/cc @sferik @hsbt

[ci skip]

script/brew-publish

+#!/bin/bash
+# Usage: script/brew-publish <name> <version> [<gh-project>]
+#
+# Updates the `<name>.rb` Homebrew formula to `<version>` and sends a pull
+# request with the change.
+set -e
+
+brew_name="${1?}"
+version="${2?}"
+
+if ! type -p hub >/dev/null; then
+  "ERROR: You have to install hub to proceed." >&2
+  exit 1
+fi
+
+if [ -n "$3" ]; then
+  gh_project="github.com/${3}"
+else
+  gh_project="$(git remote -v | grep '^origin' | grep -oE 'github.com[:/][^/]+/[^/ ]+')"
+  gh_project="${gh_project%.git}"
+fi
+
+url="https://${gh_project/:/\/}/archive/${version}.tar.gz"
+
+checksum="$(curl -fsSL "$url" | shasum | awk '{print $1}')"
+
+if [ -z "$checksum" ]; then
+  echo "ERROR: calculating the checksum failed for $url" >&2
+  exit 1
+fi
+
+pushd "$(brew --prefix)"
+
+git fetch -q origin master
+
+formula="Library/Formula/${brew_name}.rb"
+sed -i.bak -E "
+  s!^(  url ).+!\\1\"${url}\"!
+  s!^(  sha1 ).+!\\1\"${checksum}\"!
+" "$formula"
+rm -f "${formula}.bak"
+
+branch="${brew_name}-${version}"
+git checkout -q -B "$branch" origin/master
+git commit -m "${brew_name} ${version#v}" -- "$formula"
+# hackish way of getting the git remote name for user's fork
+fork_remote="$(hub fork 2>&1 | grep -oE 'remote:? \S+' | tail -1 | awk '{print $2}')"
+git push -u "$fork_remote" "$branch"
+hub pull-request -m "${brew_name} ${version#v}"
+
+git checkout -q -

script/release

+#!/bin/bash
+# Usage: script/release
+#
+# - checks out the master branch
+# - changes version in `bin/ruby-build` to current date
+# - commits and tags the change
+# - pushes master + tag to GitHub
+# - opens pull request to update the Homebrew formula
+#
+# TODO: handle making multiple releases on the same date
+# TODO: publish release notes to GitHub
+
+set -e
+
+git fetch -q --tags origin master
+
+existing="$(git tag --points-at HEAD)"
+if [ -n "$existing" ]; then
+  echo "Aborting: HEAD is already tagged as '${existing}'" >&2
+  exit 1
+fi
+
+git checkout -q master
+
+binfile="bin/ruby-build"
+new_version="$(date '+%Y%m%d')"
+version_tag="v${new_version}"
+previous_tag="$(git tag | grep '^v' | sort | tail -1)"
+
+if git diff --quiet "${previous_tag}..HEAD" -- bin share; then
+  echo "Aborting: No features to release since '${previous_tag}'" >&2
+  exit 1
+fi
+
+# current="$($binfile --version | awk '{print $2}')"
+
+sed -i.bak -E "s!^(RUBY_BUILD_VERSION=).+!\\1\"${new_version}\"!" "$binfile"
+rm -f "${binfile}.bak"
+
+git commit -m "ruby-build ${new_version}" "$binfile"
+git tag "$version_tag"
+git push origin master "${version_tag}"
+
+# git log --no-merges --format='%w(0,0,2)* %B' --reverse "${previous_tag}..HEAD^" -- bin share
+
+script/brew-publish ruby-build "$version_tag"