Grammar corrections
Delete pragma Unreferenced, and use return values
Fix Ada.Processes.Shell to raise Name_Error when the execution of the shell failed
Use < 0 instead of = -1 for return values of system calls
Fix a bug of mismatched lengths of Ada.Characters.Normalization, again
Insert pragma No_Return for __builtin_unreachable
Fix pragma Assert of Ada.Text_IO.Editing
Use pragma Check instead of pragma Assert
Improve Character'Image and 'Width