option('image_library', type: 'combo', choices: ['auto', 'gdk-pixbuf', 'qt4', 'qt5'],
       description: 'Which image processing backend to use')
option('introspection', type : 'boolean', value : 'true',
       description : 'Enable / disable the GObject-Introspection integration')
option('vapi', type : 'boolean', value : 'true')
option('tests', type : 'boolean', value : 'true',
       description : 'Enable / disable unit tests')
option('gtk_doc',
  type: 'boolean',
  value: 'false',
  description: 'Build the API reference (requires gtk-doc)')