v0.4.0

This new release is a major upgrade in that it includes:

The new IPC client from ethereumex. Which decreased test times by 5x

ExW3.tx_receipt now returns an {:ok, receipt} tuple

call_async/send_async were removed. The reason being that the blockchain connection is always the bottleneck, and users can figure out their own concurrency approach. If there is a solution that people converge on, I'm happy to incorporate it.