v0.2.0

This release, apart from internal refactoring of the code, introduces a slight change in how Mir behaves towards its application:

1. At the beginning of each epoch, it invokes the NewEpoch callback. Before this call was omitted in epoch 0 and when restoring state.
2. The nodes that propose transactions are now selected differently. If a node is suspected of being faulty (even if it is falsely), it might be suspended from proposing transactions.