[Feature Request] Overview mode in bespoke template

[arseru]

Hi all,

Following discussion in marp-team/marp#326, I would like to request a feature for an overview mode that allows to navigate easily between slides in the bespoke template (see example in revealjs).

I think it would be a nice addition since the bespoke template is already adding many features that make it feasible for a presentation tool in HTML (e.g. presenter mode, OSC, transitions, etc), and a mode that allows to quickly move between slides would be nice for larger presentations.

I'll just leave it here for the time being, maybe when I get more free time I can learn a bit of typescript and try to create a pull request for it :)

Thanks for all the hard work you put into marp every day!