Add Task.parSequence and Task.parTraverse aliases

[Avasil]

Task.parSequence = Task.gather
Task.parTraverse = Task.wander

[alexandru]

I'm starting to dislike the proliferation of aliases in Monix.

WDYT? Should we deprecate the old names? We'll keep them for binary compatibility of course.

[Avasil]

I'm fine with deprecation in this example.
I suppose we should add parXXXUnordered and parXXXN as well?
I think in Cats it's called parUnorderedTraverse but we use wanderUnordered and wanderN

1. If we are consistent with ourselves:
   parTraverse, parTraverseN, parTraverseUnordered

2. If we are consistent with Cats:
   parTraverse, parTraverseN, parUnorderedTraverse

It's unfortunate but I would go with 1 because discoverability seems to be better

[jozic]

+1 for parTraverseUnordered

[jozic]

I'll take this if no objections