Refactor code for printing directories

[joelim-work]

Fixes #602, Fixes #889

Changes:

• Calculate window width correctly when drawbox is enabled. For example, the default configuration contains three windows (shaped like | 1 | 2 | 3 |), so four spaces needs to be subtracted from the screen width, but the current implementation only subtracts one space from the last window.
• The renew function now calls getWins directly, instead of executing its own code which does the same thing.
• A maxlength variable is defined to indicate the maximum amount of space for displaying a filename, including the icon, the filename itself and the file info. This is the space left over from the window width after subtracting the space for line numbers and the select marker.

I have tested this using various combinations of settings including drawbox, number, relativenumber and icons. I would appreciate it if anyone else has the time to test this as well.

[jackielii]

Not sure if it's related, but I had to subtract image preview width by one in Tmux setup: #1143

[joelim-work]

Not sure if it's related, but I had to subtract image preview width by one in Tmux setup: #1143

@jackielii Yes, that is the same issue. Hopefully this patch should fix that particular problem for you.

[gokcehan]

@joelim-work Thanks for the patch. I hope this won't break anything else.