Refactor to `configService` to read & write `Config`

`configService` can save and load `Config` using a strategy of `configEncoder` and `configDecoder`. This pave the path for swapping out `tomlConfigEncoder` and `tomlConfigDecoder` with `yamlConfigEncoder` and `yamlConfigDecoder`.

`Configs` also has been renamed to `Config`.
Merge pull request #620 from github/gh_yaml

Refactor to `configService` to read & write `Config`