feat(kff.Collection): add map() function according to Array.map
feat(kff.Collection): add reduce() and reduceRight() function according to Array.reduce() and Array.reduceRight()
feat(kff.Collection): add slice() method according to Array.slice()
feat(kff.Collection): add push() method according to Array.push()
feat(kff.Collection): add pop() method according to Array.pop()
feat(kff.Collection): add shift() method according to Array.shift()
feat(kff.Collection): add unshift() method according to Array.unshift()