Add variable setting, instead of command for BufExplorerVerticalSplit

[KiranHappy]

Add variable setting, instead of command for BufExplorerVerticalSplit
This will help using ToggleBufExplorer command to toggle any kind of explorer horizontal or vertical and serve it's purpose.
e.g. once into vimrc a valiable is set , default position to open is set then we can use ToggleBufExplorer to open and close it at same place. wouldn't need two commands, one to open and other to close.