adding templating capabilty for config.json

[webcoderz]

No description provided.

[SecretiveShell]

Closing this as it breaks all config loaders other then config.json (invalid config.json is made if missing env vars), and is a breaking change for users using config.json due to them needing to setup their containers differently. I have included this functionality in #41 in a way that doesn't break the existing logic which should cover your workflow in a style that requires you to maintain much less complex config logic.