Investigate merge issues

[SomeKittens]

Looks like .merge is broken in latest:

let noop = () => {};
gustav.source('intv', () => Observable.interval(100));
gustav.transformer('doo', iO => iO.do(noop))
gustav.sink('tapper', iO => iO.subscribe(noop));
gustav.sink('consooole', iO => iO.subscribe(noop));

let c0 = gustav.createWorkflow('c0')
  .source('intv')
  .transf('doo');

let c1 = gustav.createWorkflow('c1')
  .source('intv');

// TODO: MERGE BROKEN
let c = gustav.createWorkflow('manySauce')
  .from('redis', 'wikiraw')
  // .merge(c0)
  .transf('doo')
  // .merge(c1)
  .transf('doo')
  .sink('consooole');

Results in: [Error] Error: To node Symbol(doo) not registered

Fix this up and write some tests so this doesn't happen again.

[SomeKittens]

Ah, looks like the current version of .merge only works when merging in two branches of the same workflow.