Add settings framework and new settings

[somini]

Added a way to run extra commands after each jump.

Using this framework, add a way to open the current fold and to center the screen.

[thinca]

Good. I think g:visualstar_extra_commands is more simple and flexible.

let g:visualstar_extra_commands = 'zzzv'

How do you think?

[somini]

Could be. My solution is more "batteries included", but that could allow for more flexibility.

I'll set it up so that g:visualstar_extra_commands overrides any other settings, but I keep the other options too.

[thinca]

Thanks :smiley: I don't want to increase options. A lot of options make the behavior complicated. Only g:visualstar_extra_commands is enough.

[somini]

Very well. I've changed it and squashed it to a single commit.

My example of using it for opening folds and centring on the screen is on the helpfile. :D

[thinca]

Very good. Thanks!