writeZip now calles provided callback if given
writeZip now calles provided callback if given

Resolves cthackers/adm-zip#97
kadledav/adm-zip,KenanSulayman/adm-zip,delmosaurio/adm-zip,paulrutter/adm-zip,cthackers/adm-zip,bestdeveloperever/adm-zip