Refactor configuration

By storing the options instead of generating handlers, we can simply
call an instance method, instead.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Add `:ignore_nil` option

Fixes #6

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Allow nil embeds

Jsonite should be smart about not sending `nil` objects to embedded
presenter objects.

Fixes #7

Signed-off-by: Stephen Celis <stephen@stephencelis.com>