Incremental Synchronization over the Internet

• Support for incremental synchronization of compressed blockchain data over the network.
• Two-step merge of large index updates to minimize chances of big index truncate operations.
• An asynchronous http downloader maximizing network bandwidth utilization during synchronization.
• Leverage the new sync-http command in the Test it yourself section of the README.
• Introduce DT_WORKERS environment variable to override the number of worker threads.
• Introduce DT_LOG environment variable to override the location of the log file.
• Make sync-http and sync-local commands warn the user about non-fulfilled hardware requirements.
• Automatic clean-up of unmerged index chunks on sync start
• Make tx-info command show human-readable output instead of JSON.
• Various optimizations and bug fixes.