Support line wrapping

[brouberol]

By using a command, such as :wrap or :linewrap, we'd split lines exceeding the terminal width over multiple terminal lines.

This will probably be complex, as it'll have an impact on line numbering, the go_to_x_y mechanism, etc, so we'd need to find a lightweight solution to compute a document coordinate / terminal coordinate mapping, instead of re-computing it everytime, which would make every coordinate jump O(n).