add lowercase + basic way to migrate config

[april-ivy]

adds something to allow the user to make the output lowercase + basic migration

initially if the user had an older vers with a diff config with missing fields etc, it'll return an error such as

Error: Error { message: "missing field `lowercase`", input: Some("[display]\nascii = \"stack\"\nseperator = \": \"\nmodules = [\"os\", \"desktop\", \"shell\", \"uptime\"]\n\n[colours]\nprimary = \"\\u001B[39m\"\naccent = \"\\u001B[36m\"\n"), keys: ["display"], span: Some(0..9) }

now it will automatically migrate configs