libtorrent-2.0.6

Changes since 2.0.5:

• fix issue creating a v2 torrent from torrent_info containing an empty file
• make recheck files also update which files use partfile
• add write_through disk_io_write_mode, which flushes pieces to disk immediately
• improve copy file function to preserve sparse regions (when supported)
• add function to truncate over-sized files part of a torrent
• fix directory creation on windows shared folders
• add flag to make add_files() not record file attributes
• deprecate (unused) allow_partial_disk_writes settings
• fix disk-full error reporting in mmap_disk_io
• fixed similar-torrents feature for v2 torrents
• fix potential unbounded recursion in add_completed_job, in disk I/O
• deprecated (unused) volatile_read_cache setting
• fix part files being marked as hidden on windows