Add support to API versioning

[dpecos]

Given a nexus path, it could be useful to pull / push tasks to that path for an specific version.

The idea could be something like:

client.pullTask("test.fibonacci", "{version: 2}") // will only pull tasks for that version client.pushTask("test.fibonacci", "{version: 1.5})" // this task won't be pulled by previous pullTask

[jaracil]

It is difficult to implement because two versions "listens" on same path.
A work around may be adding version info at the end of path.

client.pullTask("test.fibonacci.v2") // will only pull tasks for that version
client.pushTask("test.fibonacci.v2") // this task will be pulled by previous