Ability to add custom functions

[jason-johnson]

What problem are you facing?

Currently terraform-docs has a few builtin functions that can be called from the content template. There is currently a plugin that can be used but it seems to be for doing the entire formatting. Sometimes all that is needed is the ability to define new functions for the template (e.g. regex, titles, etc.).

How could terraform-docs help solve your problem?

Allow either the current plugin mechanism or a new one to define functions that will be available for the templates.