Implement simple chain/do syntax

[tshemsedinov]

const c1 = metasync.chain()
  .do(readConfig, 'myConfig')
  .do(selectFromDb, 'select * from cities')
  .do(getHttpPage, 'http://kpi.ua')
  .do(readFile, 'README.md');

c1((err, data) => {});