vertLine method
Set vertical line to screen matrix
Implementation
void vertLine(int _x, _y, count) {
String _newS;
int toX = (_x + count).toInt(); // howTo NULL check YES
for (var x = _x; x < toX; x++) {
_newS = tl.changeLetter(_matrix[x], _y, '|');
_matrix[x] = _newS;
}
}