First step: Create temporary symlinks to relocate under sites/handbook/source,
in order to get sub-site's build functional without actually
moving all the files.

Add monorepo build for sites/handbook/config.rb

require plantuml, it is needed for handbook

Add SourceWatcher monkeypatch to pick up partials under 'includes'

Account for svg images called as partials from common includes

switch to 'only:' in 'source/layouts' files.watch, to prevent build errors.

add 'duplicate_relative_prefix' option for images (to fix customer-logos-transparent.html.haml)

require mermaid in monorepo handbook site config

move compensation-roadmaps proxy handling for monorepo handbook site

move projects proxy handling for monorepo handbook site

use Middleman extension with manipulate_resource_list to avoid using config[:ignored_sitemap_matchers]

Add comment about using site-specific instead of common includes

Move build of handbook/engineering|marketing...