Replace entity.name.downcase with "#{resource.singular}"

Probably a copy paste bug
Fix bug where HTTP delete routes were not created.

ACTIONS are defined as ```[:create, :read, :update, :destroy]``` but
HTTP delete routes depended on a ```:delete``` key being present.

Changed ```:delete``` to ```:destroy``` as defined in the ACTIONS array.
Sequel adapter delegates crud! messages to crud methods.

It seems like Sequel::Model doesn't have bang versions of :create,
:update and :destroy, so I changed the sequel adapter to delegate
those calls to the appropriate non-bang implementations.
Add basic support for Last-Modified HTTP header.

```Rack::Scaffold``` checks if the used adapter does timestamping, and if so, uses
the most recent value of a generic ```updated_at_field``` for the
Last-Modified header.
Allow enabling and configuring of Sequel Timestamps plugin

CoreData adapter now looks for a :timestamps option and uses it to
configure the Sequel::Plugins::Timestamps plugin.

This allows a Helios user to do something like this:

service :data, model: Dir['*.xcdatamodel*'].first, timestamps: {create: :createdAt, update: :updatedAt}
Fix singular resource name for Sequel and CoreData adapters

Use entity.name as the Classname for dynamically generated
Sequel::Models.

Implement singular to demodulize and downcase the class.name
Merge pull request #1 from bartvandendriessche/fix/crud

Fix a few bugs that snuck in when generalizing from rack-core-data