Rename piece_attacks_from() in attacks_from()

Rename piece_attacks_from() in attacks_from()

It is in line with attackers_to() and is shorter and
piece is already redundant because is passed as template
parameter anyway.

Integrate also pawn_attacks_from() in the attacks_from()
family so to have an uniform attack info API.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>