• Add method get_with_prefix_length to the reader

• change exceptions (ArgumentError => IPAddressError)

• back to Sija/ipaddress.cr realisation
• cache with mutex
• fix #12

• fix float types

1. changed MaxMindDB::Any to crystal.datum version
2. fixed warning on Reader

1. Thread-safe cache
2. Drop sija/ip_address.cr dependency

Thanks @636f7374

Now Crystal 0.31.0 uses // by default for integer division (#2, thanks @gewo)