Lot of changes

use Symbol vs uid & simple set vs define enumerable: false if possible

Symbol constructor don't work with `new`
add Symbol.pure
add Symbol.set
remove Object.symbol -> use Symbol.pure
remove Object.hidden -> use Symbol.set

{Array::, Array}.contains & Dict.contains use SameValueZero

IE8- Object.getOwnPropertyNames fix
IE8- Object.getPrototypeOf fix
IE7mode fix (src/core.js#218, wtf?)
IE7mode setImmediate fix

add Object.getOwnPropertyKeys
fix Object.getOwnPropertyDescriptors
optimize: Object.make don't work with descriptors & enumerable: false
properties

add Dict.delete

remove Object.isEnumerable