* Migrate to GEO IP 2, because support will drop in April
* Change all links of maxmind to https
* Update maxmind database dependency and add javatar to extract
the database from the tar archive
(now only a small difference in jar file size -> ~80KB smaller)
* Verify downloaded archive using MD5 (There are no other checksums available)
* Migrate to Java NIO instead of old java file I/O (Feedback?)
* Internal Optional usage for nullable values (Feedback?)
Minor:
* Schedule a Bukkit async task instead of creating a thread manually
* Validate ip input string
* Extract validation into single method
* Close all resources safely using try-resources
* More https links
* Add documentation
* Set the same last modification as in the tar archive
* Fix tests
* Comment how the legacy API responded to unknown entries
* Document missing function param
* Document our maxmind dependency modifications
* Include time unit into constant
* More logging for downloading the database
* Add missing return if the database cannot be found
* Delete temporarily file after working with it
