message: Internal multi-threading is now implemented
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  @@ -16,7 +15,7 @@ You can slice the data frame and instead of getting another data frame you can o
  <B>Multithreading</B><BR>
  Instances of DataFrame are not multithreaded safe. In other words, a single instance of DataFrame must not be used in multiple threads without protection. But DataFrame utilizes multithreading in two different ways:<BR>
  1. There are asynchronous versions of some methods. For example, you have both sort() and sort_async(). The latter returns a std::future which could execute in parallel.
  -2. [Not fully implemented yet] DataFrame uses multiple threads, internally and unbeknown to the user, in some of its algorithms when appropriate. User can control (or turn off) the multithreading by calling set_thread_level() which sets the max number of threads to be used. The default is 0. The optimal number of threads is a function of users hardware/software environment and usually obtained by trail and error. set_thread_level() and threading level in general is a static property and once set, it applies to all instances.
  +2. DataFrame uses multiple threads, internally and unbeknown to the user, in some of its algorithms when appropriate. User can control (or turn off) the multithreading by calling set_thread_level() which sets the max number of threads to be used. The default is 0. The optimal number of threads is a function of users hardware/software environment and usually obtained by trail and error. set_thread_level() and threading level in general is a static property and once set, it applies to all instances.
  <B>Example Code</B><BR>
  