To help user write callbacks (e.g. before_send, before_breadcrumb, and trace_sampler) and customize tracing features, we should provide better documentation about the objects they'll deal with. Which will be:

• Delegated top-level methods, e.g. Sentry.set_user
• Sentry::Transaction
• Sentry::Span
• Sentry::Client
• Sentry::Scope
• Sentry::Event
  • Sentry::RequestInterface
• Sentry::TransactionEvent
• Sentry::Breadcrumb