Custom Placeholders from API/EssentialsX variables

[caramelpony]

I'd love to see the addition of a %user_mail_count% placeholder, to allow frequenting users to see pending mail. Small variables like that, and also the ability to add custom placeholders from an API, so like

//Pre-requisite values for the below mentioned APIs.
"token" = "SomeTokenToAllowAPIAcess"
"userUUID" = player.UUID


//Placeholders and such
"%example1%" = "https://example.com/apiv2/{token}/user/{userUUID}/serverVar"

So, %example1% would be referring to the about URL, and allow the server owner to define some pre-requisite info that might need to be provided for the API