Added macro for defining gc callbacks.
Added macro for defining gc callbacks.

noahjs/nan,lovell/nan,mscdex/nan,mikolalysenko/nan,durai145/nan,durai145/nan,lovell/nan,hmalphettes/nan,thefourtheye/nan,fleg/nan,guymguym/nan,thejinx0r/nan,mikolalysenko/nan,noahjs/nan,hmalphettes/nan,thejinx0r/nan,eljefedelrodeodeljefe/nan,Jonekee/nan,Jonekee/nan,eljefedelrodeodeljefe/nan,durai145/nan,sesh-kebab/nan,evanlucas/nan,ipmobiletech/nan,saper/nan,mikolalysenko/nan,sanemat/nan,evanlucas/nan,addaleax/nan,gastrodia/nan,fleg/nan,gagern/nan,mscdex/nan,mscdex/nan,saper/nan,ipmobiletech/nan,ipmobiletech/nan,LinusU/nan,sesh-kebab/nan,eljefedelrodeodeljefe/nan,evanlucas/nan,durai145/nan,thejinx0r/nan,sanemat/nan,thefourtheye/nan,sesh-kebab/nan,thefourtheye/nan,evanlucas/nan,LinusU/nan,addaleax/nan,Jonekee/nan,hmalphettes/nan,nodejs/nan,hmalphettes/nan,noahjs/nan,nodejs/nan,LinusU/nan,saper/nan,gastrodia/nan,LinusU/nan,lovell/nan,guymguym/nan,guymguym/nan,addaleax/nan,saper/nan,mikolalysenko/nan,fleg/nan,lovell/nan,ipmobiletech/nan,gagern/nan,sanemat/nan,gagern/nan,guymguym/nan,thejinx0r/nan,sanemat/nan,gastrodia/nan,thefourtheye/nan,noahjs/nan,eljefedelrodeodeljefe/nan,sesh-kebab/nan,nodejs/nan,nodejs/nan,addaleax/nan,mscdex/nan,fleg/nan,gastrodia/nan,Jonekee/nan