Named fragment API

[timkendall]

Possible API:

// or class-based API

const userName = new Fragment({
  name: 'UserDetails',
  on: 'User',
  selection: (t) => [ t.name(t => [ t.first(), t.last() ]) ]
})

// higher-level functional API
const userName = on('User', t => [ t.name(t => [ t.first(), t.last() ])).named('UserNameFields')
// or
const userName = user(t => [ t.name(t => [ t.first(), t.last() ])).toFragment('UserNameFields')