Database adapters: Multi updates

multi-adapter.js

const service = require('feathers-<database>');

// Allow multi create, patch and remove
service({
  multi: true
});

// Only allow create with an array
service({
  multi: [ 'create' ]
});

// Only allow multi patch and remove (with `id` set to `null`)
service({
  multi: [ 'patch', 'remove' ]
});