Add expose SYMBOL, HASH BLOCK

[fahchen]

expose :last_reply, :using => API::Status do |status, options|
  status.replies.last
end

Use the block result as the object and represent it with using_options

[dblock]

Is this just another syntax for expose :symbol, { :proc => }? Can't all this be accomplished with existing options?

[dblock]

Also, would you please be so kind to update CHANGELOG. Thx.

[fahchen]

This can use the block result as the object and represent it with :using option.

[dblock]

Merged, thank you.