added bulk create method for posting 1+ N tasks in single api call

[Stephenitis]

The api allows for bulk posting of tasks but the ruby but the tasks.create method was not changeable to fit this behavior without possibly breaking code where previous users would have an array as their payload rather than an array of payloads.

p client.tasks.bulk_create('hello_ruby', Array.new(100) {|i| {:hello => "world"} }, {:cluster => "mem1"} )

[ysadka]

:+1:

[Stephenitis]

@sunloverz can you review implementation?

[sunloverz]

@Stephenitis any updates here?

[ysadka]

@Stephenitis ping. wanna get this merged?

[treeder]

Can you guys get this into iron_worker_ruby too (nearly the same code, was copied over). https://github.com/iron-io/iron_worker_ruby

NG will probably be deprecated soon.