Change Rollbar::Configuration#use_sidekiq and Rollbar::Delay::Sidekiq api

Rollbar::Delay::Sidekiq now respond to #call which allows it to be bound to `Rollbar::Configuration#async_handler`.
Cleans up Rollbar::Configuration api: use sidekiq by calling `#use_sidekiq(options)` instead of `#use_sidekiq=(options)`.
Rollbar::Delay::Sidekiq specs are now isolated.
Change Rollbar::Configuration#use_sucker_punch and Rollbar::Delay::SuckerPunch to match previous async API changes.

Added SuckerPunch spec
More explicit `Rollbar::Configuration#use_sidekiq` signature
Added guard and deprecation warning 

..around `Rollbar::Configuration#use_sidekiq=` and `Rollbar::Configuration#use_sucker_punch=` to match new syntax.
Fix specs with Ruby 1.8
use new syntax for #use_sucker_punch in specs
Fix specs with Ruby 1.8.X
Stick to hash-rocket style hashes for Ruby 1.8.X
Don't run Rollbar::Delay::* specs with Ruby 1.8.7
Merge pull request #73 from jeremyvdw/enhanced_sidekiq_configuration

Enhanced Sidekiq and SuckerPunch configuration