Extending the calc.js module to cater for a 3x15_21

[lule75]

Hello Philhag there is an experimental scoring by BWF for a 3x15_21 similar to your #45 . kindly update your calc.js file to cater for this scheme.
I made the following changes offline to make it work.

...if (counting === '3x15_21') {
return (
((candidate == 15) && (other < 14)) ||
((candidate > 15) && (candidate <= 21) && (other == candidate - 2)) ||
(candidate == 21) && (other == 20)
);
}

@game_winner

... } else if (counting === '3x15_21') {
if ((left_score < 15) && (right_score < 15)) {
return 'inprogress';
}
if ((left_score < 21) && (right_score >= left_score - 1) && (right_score <= left_score + 1)) {
return 'inprogress';
}
}
@winning_game_count
Most 3-game series use 2 wins:
...
case '3x15_21':
return 2;

@max_game_count
Most 3-game series max at 3:

... case '3x15_21':
return 3;

recalc_after_score (interval detection)
Add the interval logic (midpoint) for "3x15_21". Assuming midpoint at 8 points (similar to other 3x15 variants):

} else if (counting === '3x15_21') {
is_interval = (
(s.game.score[team_id] === 8) && (s.game.score[1 - team_id] < 8)
);
}

@NetScore
Add "3x15_21" to _finish_score rules. Max score is 21; win-by-2 if opponent ≥ 14:

....} else if (counting === '3x15_21') {
if (score[1 - winner] >= 20) {
score[winner] = 21;
} else if (score[1 - winner] >= 14) {
score[winner] = score[1 - winner] + 2;
} else {
score[winner] = 15;
}
}