Remove serialization methods

[mikeabdullah]

Since they're just tiny wrappers around NSCoding and friends, they have little purpose (we can use NSKeyedArchiver directly). I don't believe any other collection class in Cocoa has such an implementation.

[dongyuwei]

in my testcase PJTernarySearchTree * tree = [NSKeyedUnarchiver unarchiveObjectWithFile:path] is much slower than 1. read a json file to NSDictionary 2. build PJTernarySearchTree from the dict.