Clean up comments in code

- Capitalize comments
- Reformat multi-lines comments to equalize the widths of the lines
- Try to keep the width of comments around 85 characters
- Remove periods at the end of single-line comments

closes https://github.com/official-stockfish/Stockfish/pull/5469

No functional change

src/position.h

@@ -315,8 +315,8 @@ inline bool Position::capture(Move m) const {
 }
 
 // Returns true if a move is generated from the capture stage, having also
-// queen promotions covered, i.e. consistency with the capture stage move generation
-// is needed to avoid the generation of duplicate moves.
+// queen promotions covered, i.e. consistency with the capture stage move
+// generation is needed to avoid the generation of duplicate moves.
 inline bool Position::capture_stage(Move m) const {
     assert(m.is_ok());
     return capture(m) || m.promotion_type() == QUEEN;