Add rake task to cut releases

Gemfile

@@ -4,6 +4,7 @@ source 'https://rubygems.org'
 
 gemspec
 
+gem 'bump', require: false
 gem 'pry'
 gem 'rake', '~> 12.0'
 gem 'rspec', '~> 3.7'

tasks/cut_release.rake

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'bump'
+
+namespace :cut_release do
+  %w[major minor patch pre].each do |release_type|
+    desc "Cut a new #{release_type} release, create release notes " \
+         'and update documents.'
+    task release_type do
+      run(release_type)
+    end
+  end
+
+  def add_header_to_changelog(version)
+    changelog = File.read('CHANGELOG.md')
+    head, tail = changelog.split("## master (unreleased)\n\n", 2)
+
+    File.open('CHANGELOG.md', 'w') do |f|
+      f << head
+      f << "## master (unreleased)\n\n"
+      f << "## #{version} (#{Time.now.strftime('%F')})\n\n"
+      f << tail
+    end
+  end
+
+  def run(release_type)
+    old_version = Bump::Bump.current
+    Bump::Bump.run(release_type, commit: false, bundle: false, tag: false)
+    new_version = Bump::Bump.current
+
+    add_header_to_changelog(new_version)
+
+    puts "Changed version from #{old_version} to #{new_version}."
+  end
+end