remove blank line between function and it's description

- remove the blank line between the declaration of the function and it's
  comment, leads to better IDE support when hovering over a function to see it's
  description
- remove the unnecessary duplication of the function name in the functions
  description
- slightly refactored code for lsb, msb in bitboard.h There are still a few
  things we can be improved later on, move the description of a function where
  it was declared (instead of implemented) and add descriptions to functions
  which are behind macros ifdefs

closes https://github.com/official-stockfish/Stockfish/pull/4840

No functional change

src/thread.h

@@ -38,7 +38,6 @@ namespace Stockfish {
 // per-thread pawn and material hash tables so that once we get a
 // pointer to an entry its lifetime is unlimited and we don't have
 // to care about someone changing the entry under our feet.
-
 class Thread {
 
     std::mutex              mutex;
@@ -76,7 +75,6 @@ class Thread {
 
 
 // MainThread is a derived class specific for main thread
-
 struct MainThread: public Thread {
 
     using Thread::Thread;
@@ -97,7 +95,6 @@ struct MainThread: public Thread {
 // ThreadPool struct handles all the threads-related stuff like init, starting,
 // parking and, most importantly, launching a thread. All the access to threads
 // is done through this class.
-
 struct ThreadPool {
 
     void start_thinking(Position&, StateListPtr&, const Search::LimitsType&, bool = false);