Add ClosedOrders API call (https://www.kraken.com/help/api#get-closed-orders)
Do not include .gem files in themselves.
Create a more granular nonce to prevent EAPI:invalid nonce errors
Merge branches 'add_closed_orders', 'fix_gemspec' and 'more_granular_nonce'

* add_closed_orders:
  Add ClosedOrders API call (https://www.kraken.com/help/api#get-closed-orders)

* fix_gemspec:
  Do not include .gem files in themselves.

* more_granular_nonce:
  Create a more granular nonce to prevent EAPI:invalid nonce errors