Update to 0.15.0:

• raft_io version 2 introducing async_work
• raft_fsm version introducing snapshot_async
• Disable failing test for libuv 1.44.2 and higher
• Support for automated recovery of corrupt segments upon startup. When detecting a corrupt segment, raft will rename the segment to corrupt-{timestamp}-{original-name} and attempt to start again, once. This behaviour can be disabled with raft_uv_set_auto_recovery.
• Support for raft_uv_tcp_set_bind_address
• Deprecate raft_fixture_init, use raft_fixture_initialize combined with raft_fixture_grow
• Move to raft_fsm v2 introducing snapshot_finalize. snapshot_finalize, if not NULL this is run after a successful call to snapshot and must be used to cleanup state introduced by snapshot a.o. freeing allocated memory, releasing locks, etc. If snapshot_finalize is set, raft is no longer an owner of the raft_buffer array returned by snapshot. This change unfortunately breaks binary compatibility and builds libraft.so.2 instead of libraft.so.0.