Complete set of can-symbol registered symbols

With this release, can-list implements the symbols:

• @@can.splice: pointing to the .splice() function
• @@can.updateDeep and @@can.assignDeep: calls can-reflect.updateDeepList()
• @@can.getOwnEnumerableKeys: returns all integer indexes and all keys pointing to data elements
• @@can.unwrap: equivalent to calling .attr() with no arguments
• @@can.serialize equivalent to .serialize()
• @@can.onKeysAdded and @@can.onKeysRemoved: triggers the callback when new keys or indexes are added or removed, respectively.