Print banner text re v3.0.0 when zip is required.

lib/zip.rb

@@ -34,6 +34,25 @@
 require 'zip/errors'
 
 module Zip
+  BANNER = [
+    'RubyZip 3.0 is coming!',
+    '**********************',
+    '',
+    'The public API of some Rubyzip classes has been modernized to use named',
+    'parameters for optional arguments. Please check your usage of the',
+    'following classes:',
+    ' * `Zip::File`',
+    ' * `Zip::Entry`',
+    ' * `Zip::InputStream`',
+    ' * `Zip::OutputStream`',
+    '',
+    'Please ensure that your Gemfiles and .gemspecs are suitably restrictive',
+    'to avoid an unexpected breakage when 3.0 is released (e.g. ~> 2.3.0).',
+    'See https://github.com/rubyzip/rubyzip for details. The Changelog also',
+    'lists other enhancements and bugfixes that have been implemented since',
+    'version 2.3.0.'
+  ].freeze
+
   extend self
   attr_accessor :unicode_names,
                 :on_exists_proc,
@@ -47,6 +66,8 @@ module Zip
                 :validate_entry_sizes
 
   def reset!
+    warn BANNER.join("\n") unless BANNER.empty?
+
     @_ran_once = false
     @unicode_names = false
     @on_exists_proc = false