* final engine changes
* migration to v13
* adding and removing pending transitions
* epoch_transition_for
* port snapshot to new engine methods
* final validator set interface
* fix compiler errors
* revert v13/epoch_depth transition
* make call on new epoch
* rolling finality checker
* tests for finality checker
* constructing finality proof upon pending transition
* fix warnings and finality proof checking
* fix compiler warnings in tests
* test fixes
* don't include genesis in finality checking
* change snapshot test chain building logic
* minor refactorings
* fetch epoch transition based on parent, fix divide-by-zero in SimpleList
* fix formatting
* fix ABIs and finality checking in snapshot restoration
* encode signal number in proof
* create more blocks at the end of tests
* update gist to accurate contract code
* test for epoch_transition_for
* fix tests with immediateTransitions parameter
* disable force flag after forcing
* rename ValidatorsChanged to InitiateChange and finalizeSignal to finalizeChange
* a few more validator set tests
* separate modules for consensus snapshot chunks
* bulk of authority warp logic
* finish authority warp implementation
* squash warnings and enable authority snapshot mode
* test harness for PoA
* fiddle with harness
* epoch generation proof fixes
* update constructor code
* store epoch transition proof after block commit
* basic snap and restore test
* use keyvaluedb in state restoration
* decompress chunks
* fix encoding issues
* fixed-to-contract-to-contract test
* implement ancient block import
* restore genesis transition in PoW snapshot
* add format version method to snapshot components
* supported version numbers in snapshot_components
* allow returning of ancient epoch transitions
* genesis hash mismatch check
* remove commented code
