Added test for blocked piece.
Added potentially dangerous (but probably working) implementation to prevent moves at blocked positions
Queen test added
Opponent's pawn blocks moving test.
Take into account possibility to move forward if the destination square is not busy.
Extracted utility to check belonging to the same file.
Second move busy is covered
Double-move test shows we don't prevent move if intermediate position is occupied
Hard way to detect impossible double move of pawn when the middle square is busy.
Test for blocking black pawn's double move.
Filter out double moves if intermediate square is busy
Some comment....
Test shows we don't validate promotion possibility
Promoitions are also covered by blocked conditions.
Merge pull request #45 from lrozenblyum/PawnMovement

Pawn movement Fixes #44