Contract and account now both have an address field or method for the
sake of simplicity.

Transactions can no longer serve as callers. Accounts are now the
initial callee of closures. Transactions now serve as transport to call
closures.

Status: Work in progress

Clients can set their own client string which will be send to connected
peers during the handshake.

The Ethereum structure now complies to a EthManager interface which is
being used by the tx pool, block manager and block chain in order to
gain access to each other. It's become simpeler.
TODO: BlockManager => StateManager

Rename .travil.yml to .travis.yml