Recursive directory processing, removal of deprecated features

This change primarily introduces full recursive directory processing and removes all currently deprecated features. Scenario coverage is added for template generation, both for built-in templates and custom template providers. I've also tidied up the formatting and wording in the change log.

In the code, the most notable change is the removal of `Project.config_dir` as this concept is obsolete given we blanket process any file with a '.dice' extension that we come across.

I've not bumped the version number yet as we don't know what it will be and the change log makes it clear that the changes are present on the develop branch. This seems to be the prevailing pattern of operation in projects like Cucumber and RSpec.