Fixed a discrepancy between buffer's .hpp .cpp

The Buffer constructor takes a filename for its only parameter.
The hpp constructor's parameter name was "text" instead of "filename".
One-lined increment/decrement of cursor position.

I put the increment/decrement of the cursor position as part of
the move function's parameters.

i.e.
Doing this:
move(--cur_y, cur_x);

Instead of this:
cur_y--;
move(cur_y, cur_x);