Open :members in the same window by default

[VAWVAW]

Afaik :members is the only command that opens a split. This is disrupting for a workflow that uses only one window and the jumplist.

The old behavior can be recreated using the macro :rightb :vs<Enter>:vert :res 30<Enter>:members<Enter>.

[ulyssa]

I think I've convinced myself that opening in the same window is the better default. I originally made it a split to allow for a sidebar type of view, but the default width of 30 columns means that it's never quite wind enough for some display names.

Making it open in the same window by default should hopefully be a better flow. I've added a settings.members_split option which can force a split instead, and also updated the PR to use cmd.switch for generating the action, so that something like :vert members can override it.