Add l as an additional key to select a buffer

[atsenev]

Hello. By using terminal file managers like lf and ranger I got used to opening files by pressing "l". So I created a fork and added this feature to bufexplorer too. If you think that other people might find it useful too and it it's ok to make it work like that by default I can create a PR and merge my changes.

[jlanzarotta]

Hello. Let me take a look at it. Sounds interesting.