flag-equal config file

[meowsbits]

geth accepts a flag --config which gets marshaled into a special data type. https://github.com/ethereum/go-ethereum/blob/master/eth/config.go#L90

Maybe also supported should be an --config.flags path which would provide a direct mapping for a toml config file (not the same as other existing --config file) to app flags, which could be implemented at the level of the cli.App.