some changes in Engine, LabyrinthBoard classes

In Documentation file points:
1.d. Removed some not necessary comments.

2.h. Set capital letters in constant LabyrinthSize
i. Created new constant PIECEPOSITION for piece of position for initial
row and column equal to 3.
j. Removed the key work “this” in properties PiecePositionRow and
PiecePositionCol
k. Changed the name of ll to labyrinth.

3.
d. Renamed the variable _continue with correct name flagContinue.
e. Renamed the variable ll with correct name labyrinth.
f. Removed the rest of the occurrences of private i=0, j=0,m=3,n=3.
g. Changed the if (input.Length > 1 || input.Length == 0) with short
boolean expression input.Length == 1.
h. Created two new methods ProcessInputDirection(input) and
ProcessInputCommand(input) for process input command or direction from
the user.
i. Created new method WalkInLabirinth() – moved here all doubled logic
for checking of the new cell or exit.
j. Crated method Restart () with initialization of the flagContinue for
every time when this method is called. Used when needed ‘restart’.