feat(core): split raw client and managed client as well as packet handlers

Resolves #65

Merge pull request #60 from Rutherther/feat/combat-v1

Make combat nonblocking, make multiple queues for distinct operations

feat(game): cancel the skill contract in case no response is obtained

Merge pull request #55 from Rutherther/feat/contracts

Add contract system

feat(game): split nostale apis into safe, unsafe, add contracts usage