1.6.0

• 1.5.0 and 1.5.1 contained a possible memory corruptions when using
  getWithPrefixLen. This has been fixed. Reported by proton-ab.
  GitHub #96.
• The composer.json file now conflicts with all versions of the
  maxminddb C extension less than the Composer version. This is to
  reduce the chance of having an older, conflicting version of the
  extension installed. You will need to upgrade the extension before
  running composer update. Pull request by Benoît Burnichon. GitHub
  #97.