v2.0.0 release

Bug fixes:

• Peer's next log index overflow (#227).
• Config loss caused by the restart during joining cluster (#232).
• Missing configuration log during snapshot creation (#244).
• Incorrect log index in get_peer_info (#246).
• Duplicate save_state call during vote (#262).
• New member's target priority issue during catch-up (#270).
• Missing role change during pre-vote (#277).
• Memory leak caused by internal commit data (#278, #296).
• Debugging log overflows (#289, #290, #363).
• Leadership validity checking (#291).
• Race between term update and client request (#294).
• Missing commit results for auto-forwarding in async mode (#350).
• Disruptive leader election during a leadership takeover request (#357).
• Segfault during snapshot installation (#373).
• Missing RemovedFromCluster callback (#382).

Features:

• Background async snapshot IO (#228).
• New APIs to pause/resume state machine execution (#234).
• Callbacks for tracking lifecycles of ASIO worker threads (#245).
• Full consensus mode (#248).
• Selective quorum support (#263).
• Extended append_entries API (#273).
• Parallel log appending (#283).
• New API to create a snapshot manually (#360).
• Custom resolver (#361).
• Automatic timestamp generation for each log (#368).
• Randomized snapshot creation timing (#372).