Feature-ethereum

Adds rudimentary support for Ethereum blockchain lookups.
It currently assumes `ethereum`, the go client, is running, with JSON-RPC enabled. This is defaulted to port 8080 currently.

Querying the Ethereum chain requires two parameters, the address, and key. Address is the contract address to look up, and key is the storage slot within the contract to query. These parameters are currently deduced by using the root element of the URL path as the address, and the rest as the key.
ie: ethereum.dns/ADDRESS/KEY
So why isn't it used? Is rpc username/password not required as it is for Namecoin and KeyID?

You can [copy this code](https://github.com/WeMeetAgain/dnschain/blob/feature-ethereum/src/lib/config.coffee#L115-L125) and modify it as appropriate if necessary.