Add support of the environment variables to override the project configuration and global configuration (#273).

All variables will start with FXP_ASSET__ and uppercased, and each - will replaced by _.

Example:

{
    "config": {
        "fxp-asset": {
            "pattern-skip-version": "(-patch)"
        }
    }
}

Can be overrided by FXP_ASSET__PATTERN_SKIP_VERSION="(-build)" environment variable.