Added "Use One View" option

When I use your plugin to navigate, it opens too much folder views in my opinion.

So I added a use_one_view option, such that when it is true, the enter key close the current directory view before to open a new one. I kept the previous behavior by default (use_one_view:false).

For the user this looks like only one view is used.

But ! If you open Dired from one file, and then from another, you can still have multiple folder views opened.

If you agree with this new parameter, please merge.

Thanks for your plugin !