Some code and comment cleanup

- Remove all references to split points
- Some grammar and spelling fixes

No Functional change

Resolves #478

src/thread.h

@@ -57,8 +57,8 @@ struct ThreadBase : public std::thread {
 };
 
 
-/// Thread struct keeps together all the thread related stuff like locks, state
-/// and especially split points. We also use per-thread pawn and material hash
+/// Thread struct keeps together all the thread related stuff like locks, state,
+/// history and countermoves tables. We also use per-thread pawn and material hash
 /// tables so that once we get a pointer to an entry its life time is unlimited
 /// and we don't have to care about someone changing the entry under our feet.
 
@@ -106,13 +106,13 @@ struct TimerThread : public ThreadBase {
 
 
 /// ThreadPool struct handles all the threads related stuff like init, starting,
-/// parking and, most importantly, launching a slave thread at a split point.
+/// parking and, most importantly, launching a thread.
 /// All the access to shared thread data is done through this class.
 
 struct ThreadPool : public std::vector<Thread*> {
 
-  void init(); // No c'tor and d'tor, threads rely on globals that should be
-  void exit(); // initialized and are valid during the whole thread lifetime.
+  void init(); // No constructor and destructor, threads rely on globals that should 
+  void exit(); // be initialized and valid during the whole thread lifetime.
 
   MainThread* main() { return static_cast<MainThread*>(at(0)); }
   void read_uci_options();