New option "--threads" can be used to set how many parallel downloads to run. The default is 4 threads.
Changes to behavior:
- Serials and changelogs are saved and covers downloaded for all games that match the "--game" filter before any other files are downloaded.
- Automatic XML creation is run after all files are downloaded. Previously xml data was automatically created right after download finished.
- The "--limit-rate" option sets rate limit for thread not global rate limit.
