2.2.0

• Improved reflection decoding performance by skipping Unmarshaler checks for
  destination types that cannot implement the interface.
• Fixed verifier search-tree size arithmetic to match the reader's safe
  multiplication order instead of using an overflow-prone equivalent formula.
• Fixed unsigned bounds checks in search-tree node reads and traversal so very
  short malformed buffers return errors instead of underflowing the bounds
  calculation.
• Fixed the reflection decoder so pointer fields are not allocated when
  decoding fails with a type mismatch.
• Fixed Result.Prefix() to use the reader's measured IPv4 subtree depth
  instead of assuming IPv4 records always start at bit 96 in IPv6 databases.
• Fixed reflection decoding of negative int32 values into unsigned Go fields
  so it now returns a type error instead of wrapping them to large integers.
• Fixed lookups that followed malformed search-tree pointers past the data
  section so they now fail during Lookup instead of surfacing a deferred
  decode error.
• An error is returned when a maxminddb struct tag is clearly invalid (non
  UTF-8) instead of silently ignoring validation failures.
• Increased internal string cache size to 4096 entries to reduce cache thrashing
  and improve concurrent performance.