areaScrollUp method
Implementation
void areaScrollUp(int lines) {
final scrollRange = getAreaScrollRange();
for (var i = scrollRange.top; i < scrollRange.bottom; i++) {
if (i + lines < scrollRange.bottom) {
this.lines[i] = this.lines[i + lines];
} else {
this.lines[i] = _newEmptyLine();
}
}
}