ChristianMct/helium: v0.3.0

This update packages various features introduced in the last year, mostly to support project using Helium.

Added

• Circuit runtime can now access circuit Descriptor information such as the signature's arguments. This enables "runtime" arguments to be passed to circuits.
• A circuits.TestRuntime type that implements the circuits.Runtime interface for local test purposes. It provides a simplified setup/input/evaluation/output to test circuits locally without instantiating a full set of service.
• The circuits.Input type to represent circuit inputs.
• The circuits.Runtime.CircuitDescriptor method for accessing a running circuits' metadata (esp. its signature's arguments).
• The circuits.Runtime.InputSum method for efficient handling of directly-summed inputs from the session's threshold-number of parties.
• Client nodes can now submit circuit-evaluation requests.
• The node.SecretProvider interface for provisioning of the node's secret-keys.

Changed

• The compute.InputProvider interface is now called only once per circuit. It now takes as input a circuits.Descriptor instead of a single circuits.OperandLabel, and must return a channel of circuits.Input that will be consumed by the framework.