Introduce sub-(sub-)rounds to tournament round counting and PGN

[alwey]

There have been requests for a more fine-grained identification of tournament games.
This PR introduces sub-round and sub-sub-round counters to the Tournament class.
It extends the simple numerical PGN "Round" tag value like [Round "1"] to structured values, e.g. [Round "1.2.1"]. Resolves #249.

Example from PGN Specification, Section 8.1.1.4:

[Round "1"]
[Round "3.1"]
[Round "4.1.2"]

To accomplish a more fine-grained control of openings two new policy options are introduced to OpeningPolicy:

1. SubRoundPolicy which shifts openings for a new sub-round.
2. KeepPolicy which always keeps the same opening.

There a policies to shift or not shift openings for the levels of a tournament (game, encounter, sub-round, round, tournament).

 -openings file=file format=[epd | pgn] order=[random | sequential]
             plies=plies start=start policy=[default | encounter | subround |
             round | keep]
             ...
             The value of policy rules when to shift to a new opening.  If set
             to "encounter" a new opening is used for any new pair of players,
             "subround" shifts when a new sub-round begins, "round" shifts when a
             new round begins, and with "keep" the opening stays unchanged. The
             "default" shifts for any new pair of players and also when the
             specified number of opening repetitions is reached.

• The subround counting is used for round-robin tournaments. This fixes the round repetition policy mismatch where the PGN round does not correspond to a round specified by the -rounds option. Now the PGN round tag is constant for a whole cycle of sub-rounds. Those sub-rounds are numbered by the second counter. A sub-round consist of several encounters, depending on the number of players. In this PR the games within a sub-round are numbered by the sub-sub-round counter. Resolves openings policy works for gauntlet but not for round-robin (default) #641.
• For pyramid tournaments the function of the round counter is now distributed between round and sub-round counter.
• In gauntlet tournaments the sub-round counter tracks the gauntlet (seeded) players, the sub-sub-round counter individual games.
• In knockout tournaments the sub-round is constant for a pair, the sub-sub-round counts the games of a pair.

The "round" field was changed from int to QString in PgnGame.

HTH

[chesserik]

Hi! This is Erik, CEO of Chess.com. We are currently hiring for two important roles on our engineering team: Chess Explanation Engineer, and Engineering Team Lead - Analysis & Core Chess. Would you potentially be interested in either of those? If so let me know and we can discuss!

Best,

Erik
erik@chess.com