[fpc-pascal] TRegistry documentation

[Jean SUZINEAU]

I just add a small program to illustrate the type cast between signed 
and unsigned:

var
    si: ShortInt;
begin
      si:= -127;
      WriteLn( 'si ', si);
      WriteLn( 'Byte(si) ', Byte(si));
      si:= -1;
      WriteLn( 'si ', si);
      WriteLn( 'Byte(si) ', Byte(si));
end.

gives

$ ./project1
si -127
Byte(si) 129
si -1
Byte(si) 255
$