Use underscores instead of hyphens in shortcode names

[joostthehost]

According to Wordpress:

"Shortcode names should be all lowercase and use all letters, but numbers and underscores should work fine too. Be wary of using hyphens (dashes), you'll be better off not using them. "
https://codex.wordpress.org/Shortcode_API

The use of the dash in the shortcodes can throw issues with other plugins and potential custom code that sees it as an invalid shortcode (the widely used Visual Composer for example, doesn't accept shortcode names with hypens in them. It blocks users from adding those shortcodes to their setup).
More info on what exactly can go wrong when using hyphens:
https://codex.wordpress.org/Shortcode_API#Hyphens

I'm aware this change would not be backwards compatible, and would thus be a breaking change for existing installations. An option to overcome this is to do a search and replace on the database to update existing shortcodes to the new style, and displaying a message in the admin interface to notify editors of the updated shortcodes.