add implemention of binary search tree, not apply to mapreduce_lite.cc
yet
add headfile stdlib.h for binary_search_tree
fix implemention of BinarySearchTree::insert
modify CMakeLists.txt to support compile of binary_search_tree
add func to class BinarySearchTree
using BinarySearchTree insead of std::map
modify return value of get_value and fix bugs
fix bugs in BinarySearchTree::find and insert
also return *none* const value in get_value
modify CMakeLists.txt
to support class BinarySearchTree
fix wrong usage in ReduceWorker
do not sleep in main