chore: export Giveaway class

[imranbarbhuiya]

Changes

Export Giveaway class.

Why?

• You can now extend start method where Giveaway class is needed.

• You can now use a custom Manager with the giveaway class.

• You can extend Giveaway class to do any changes and then use it in GiveawayManager#start to use extended Giveaway class.

  Status

• [x] These changes have been tested and formatted properly.

• [ ] This PR includes only documentation changes (JSDoc, README or typings), no code change.

• [ ] This PR introduces some breaking changes.

[Nico105]

alright, but for the record I have to say: people who change too much in it will be on their own for bug fixing.