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/benchmark.cpp

@@ -97,7 +97,7 @@ const std::vector<std::string> Defaults = {
 
 namespace Stockfish {
 
-// setup_bench() builds a list of UCI commands to be run by bench. There
+// Builds a list of UCI commands to be run by bench. There
 // are five parameters: TT size in MB, number of search threads that
 // should be used, the limit value spent for each position, a file name
 // where to look for positions in FEN format, and the type of the limit:
@@ -108,7 +108,6 @@ namespace Stockfish {
 // bench 64 1 100000 default nodes  : search default positions for 100K nodes each
 // bench 64 4 5000 current movetime : search current position with 4 threads for 5 sec
 // bench 16 1 5 blah perft          : run a perft 5 on positions in file "blah"
-
 std::vector<std::string> setup_bench(const Position& current, std::istream& is) {
 
     std::vector<std::string> fens, list;