Fixes since the 1.2.10 release:
- fix issue with moving the session object
- deprecate torrent_status::allocating. This state is no longer used
- fix bug creating torrents with symbolic links
- remove special case to save metadata in resume data unconditionally when added throught magnet link
- fix bugs in mutable-torrent support (reusing identical files from different torrents)
- fix incorrectly inlined move-assignment of file_storage
- add session::paused flag, and the ability to construct a session in paused mode
- fix session-pause causing tracker announces to fail
- fix peer-exchange flags bug
- allow saving resume data before metadata has been downloaded (for magnet links)
- record blocks in the disk queue as downloaded in the resume data
- fix bug in set_piece_deadline() when set in a zero-priority piece
- fix issue in URL parser, causing issues with certain tracker URLs
- use a different error code than host-unreachable, when skipping tracker announces