French Advance: Milner-Barry Gambit and Sørensen Gambit

[seccohazy]

1. e4 e6 2. d4 d5 3. e5 c5 4. c3 Nc6 5. Nf3 Qb6 6. Bd3

The Milner-Barry Gambit in the French Advance gambits a pawn on d4 for quick development. The opening explorer identifies 6.Bd3 as the gambit move, but this seems premature and somewhat inaccurate — White can avoid the gambit and hold on to the pawn on the next move. (For example 6...Bd7 7. dxc5, or alternatively 6... cxd4 7. cxd4 Bd7 8. Be2).

As I understand it, and as the books talk about it, White gives up the pawn with 7.O-O — or, if Black includes 6... cxd4 7. cxd4 Bd7, it begins with the move 8. O-O.

I'm not sure if the directory even allows for two separate positions being given the same name. In that case Milner-Barry at 6. Bd3 is probably fine.

In the same line, I would also like to see the inclusion of the "Sørensen Gambit". I've seen it mentioned in John Watson's Play the French and in Viktor Moskalenko's The Even More Flexible French. It's this knight move—

1. e4 e6 2. d4 d5 3. e5 c5 4. c3 Qb6 5. Nf3 Nc6 6. Bd3 cxd4 7. cxd4 Bd7 8. O-O Nxd4 9. Ng5

Apologies for not attempting a pull request myself, thanks in advance for any help with this.

[esmith1092]

@seccohazy I opened a PR to add this line