feature: support `icon` on individual callouts

[hneutr]

Is your feature request related to a problem? Please describe.

Callouts are great for leveraging the plugin to apply custom highlights. It would be amazing if individual callouts could specify their own icon parameter, overwriting the one specified in config.quote.icon. This is definitely a minor feature request!

Describe the solution you'd like

Allow callouts to overwrite the icon parameter set in the config.quote.icon.

Describe alternatives you've considered

In my particular use-case, I don't actually want an icon on some callouts. So, an alternative would be allowing callouts to specify that no icon be rendered. Since this can be achieved with quote.icon = '', this doesn't feel like a particularly good solution, but it would work.

Additional information

As always, I appreciate the time and effort you put into this plugin — it has genuinely improved my day to day experience with Neovim.

[MeanderingProgrammer]

Added here: 1eb3b74.

For each callout you can now specify a quote_icon value.

If you want no icon to be rendered I would use a space, i.e. quote_icon = ' ', rather than the empty string.

[hneutr]

You're awesome. Thank you!