File access, promise based, Mocha

• Enable direct file access in addition to streams. Files have the benefit that it allows random file access (e.g. skip chunks of data) #7.
• Replace callbacks and events with promises.
  • Switch from strtok2 to strtok3
• Make use of unit-test framework, #8.
  • Used Mocha.
• Support M4A/iTunes tags, #13.