Whitelist legal job parameter types

Fix typos in readme.

Pull in rake

For those that don't have it globally...

Setting the adapter load the required gem.

Use case/when

Implemented delayed_job support

Dont need the explicit error handling -- if the require fails, it will raise exactly the error we want to communicate anyway. Also use the load path, so we can allow plugins, rather than requre_relative

Lazy-load adapters, fixes #6

 Add Sidekiq adapter/wrapper fixes #3