Ensuring Data drain in Accessor#next
Repeated tests on accessor#next causes it to fail. Fixed.
Merge branch 'master' of https://github.com/forfuture-dev/node-sequential-ids

Conflicts:
	Generator.js
	tests/test.Generator.js

Merge conflicts arising due to an earlier push and merge to the remote
repository (commit 9e517c0879ae6bbcb1a2624e946b0e0b6447306a). Solving this by:
  - keeping the test in tests/test.Generator.js
  - keeping this._online attribute for Generator (Generator.js)
  - ensuring use of keys in Generator (Generator.js)