Add option for to show 1st-lvl parent dir

[djak250]

• Toggling parentdir display_regime only shows the name of the first parent dir, rather than the full path.

[djak250]

I've found that showing the path is almost useless because it goes past the edge of the buffer view. This is especially frustrating with similarly named files in different dirs. I've added the option to only list the direct parent's name to more clearly show which buffer is which.

I'm going to keep this in my personal fork, but feel free to merge this in if you find it a useful update.

[jeetsukumaran]

Very nice addition. Thanks!