Redesign config handling, use serde instead.

[quebin31]

Going to remove the dependency on config crate to use serde + toml instead.

• [x] Config structure and substructures (templating).
• [x] Integrate with serde.
• [x] Replace all uses of old config.

More changes:

• [x] Args structure
• [x] Code clean up (new modules, logic moved)
• [x] Deprecate use of failure