Add a function to the ldoc API (available in config.ld) to pass some values to the templates.

Typical use case is to use different configuration files between local development and production deployment, using different root address. Hence, you can have a local_config.ld with:

add_config_value('html_root', 'http://localhost:8000')

and the default config.ld with:

add_config_value('html_root', 'https://doc.mydomain.com')

Then in templates, you can use $(ldoc.config.html_root) to reffer to the actual value.

Work to do if PR accepted:

• Update version number
• Update documentation

Kind.