Remove castling printout (display) limitation

[Rqnsom]

Issue/Improvement

Documentation today states:

• Castling notation can be written with both 0 and O
  • Valid example: 0-0-0 or O-O
  • When Castling turn is printed out, it will be printed with 0
    notation

The second part of the second bullet, where our library always prints out with 0 character sounds like a limitation.
What we should do is:

• when Castling Turn is constructed with 0 character, printout (display) of such turn should use the same 0 character.
• in case Castling Turn is constructed with O character, then the printout (display) of such turn should use the same O character!

How

We could simply extend Castling struct to keep info about the original character which was used for the struct construction in try_from function.