CLI: Search for a config file recursively

Check if there is a `.csscomb.json` file in process directory.
If not, go one level up and search there.
Stop in HOME dir.
If no user's config found, take a default one from our package: `config/csscomb.json`.
Merge pull request #118 from csscomb/tg/search-config

CLI: Search for a config file recursively (#68, 106)